6b4a64bafd
Privileged programs are supposed to be able to read uninitialized stack
memory (ever since 6715df8d5) but, before this patch, these accesses
were permitted inconsistently. In particular, accesses were permitted
above state->allocated_stack, but not below it. In other words, if the
stack was already "large enough", the access was permitted, but
otherwise the access was rejected instead of being allowed to "grow the
stack". This undesired rejection was happening in two places:
- in check_stack_slot_within_bounds()
- in check_stack_range_initialized()
This patch arranges for these accesses to be permitted. A bunch of tests
that were relying on the old rejection had to change; all of them were
changed to add also run unprivileged, in which case the old behavior
persists. One tests couldn't be updated - global_func16 - because it
can't run unprivileged for other reasons.
This patch also fixes the tracking of the stack size for variable-offset
reads. This second fix is bundled in the same commit as the first one
because they're inter-related. Before this patch, writes to the stack
using registers containing a variable offset (as opposed to registers
with fixed, known values) were not properly contributing to the
function's needed stack size. As a result, it was possible for a program
to verify, but then to attempt to read out-of-bounds data at runtime
because a too small stack had been allocated for it.
Each function tracks the size of the stack it needs in
bpf_subprog_info.stack_depth, which is maintained by
update_stack_depth(). For regular memory accesses, check_mem_access()
was calling update_state_depth() but it was passing in only the fixed
part of the offset register, ignoring the variable offset. This was
incorrect; the minimum possible value of that register should be used
instead.
This tracking is now fixed by centralizing the tracking of stack size in
grow_stack_state(), and by lifting the calls to grow_stack_state() to
check_stack_access_within_bounds() as suggested by Andrii. The code is
now simpler and more convincingly tracks the correct maximum stack size.
check_stack_range_initialized() can now rely on enough stack having been
allocated for the access; this helps with the fix for the first issue.
A few tests were changed to also check the stack depth computation. The
one that fails without this patch is verifier_var_off:stack_write_priv_vs_unpriv.
Fixes: 01f810ace9ed3 ("bpf: Allow variable-offset stack access")
Reported-by: Hao Sun <sunhao.th@gmail.com>
Signed-off-by: Andrei Matei <andreimatei1@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20231208032519.260451-3-andreimatei1@gmail.com
Closes: https://lore.kernel.org/bpf/CABWLsev9g8UP_c3a=1qbuZUi20tGoUXoU07FPf-5FLvhOKOY+Q@mail.gmail.com/
419 lines
12 KiB
C
419 lines
12 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Converted from tools/testing/selftests/bpf/verifier/var_off.c */
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#include <linux/bpf.h>
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#include <bpf/bpf_helpers.h>
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#include "bpf_misc.h"
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struct {
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__uint(type, BPF_MAP_TYPE_HASH);
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__uint(max_entries, 1);
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__type(key, long long);
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__type(value, long long);
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} map_hash_8b SEC(".maps");
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SEC("lwt_in")
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__description("variable-offset ctx access")
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__failure __msg("variable ctx access var_off=(0x0; 0x4)")
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__naked void variable_offset_ctx_access(void)
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{
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asm volatile (" \
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/* Get an unknown value */ \
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r2 = *(u32*)(r1 + 0); \
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/* Make it small and 4-byte aligned */ \
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r2 &= 4; \
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/* add it to skb. We now have either &skb->len or\
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* &skb->pkt_type, but we don't know which \
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*/ \
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r1 += r2; \
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/* dereference it */ \
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r0 = *(u32*)(r1 + 0); \
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exit; \
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" ::: __clobber_all);
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}
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SEC("cgroup/skb")
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__description("variable-offset stack read, priv vs unpriv")
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__success __failure_unpriv
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__msg_unpriv("R2 variable stack access prohibited for !root")
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__retval(0)
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__naked void stack_read_priv_vs_unpriv(void)
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{
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asm volatile (" \
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/* Fill the top 8 bytes of the stack */ \
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r0 = 0; \
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*(u64*)(r10 - 8) = r0; \
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/* Get an unknown value */ \
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r2 = *(u32*)(r1 + 0); \
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/* Make it small and 4-byte aligned */ \
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r2 &= 4; \
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r2 -= 8; \
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/* add it to fp. We now have either fp-4 or fp-8, but\
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* we don't know which \
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*/ \
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r2 += r10; \
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/* dereference it for a stack read */ \
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r0 = *(u32*)(r2 + 0); \
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r0 = 0; \
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exit; \
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" ::: __clobber_all);
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}
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SEC("cgroup/skb")
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__description("variable-offset stack read, uninitialized")
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__success
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__failure_unpriv __msg_unpriv("R2 variable stack access prohibited for !root")
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__naked void variable_offset_stack_read_uninitialized(void)
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{
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asm volatile (" \
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/* Get an unknown value */ \
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r2 = *(u32*)(r1 + 0); \
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/* Make it small and 4-byte aligned */ \
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r2 &= 4; \
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r2 -= 8; \
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/* add it to fp. We now have either fp-4 or fp-8, but\
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* we don't know which \
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*/ \
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r2 += r10; \
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/* dereference it for a stack read */ \
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r0 = *(u32*)(r2 + 0); \
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r0 = 0; \
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exit; \
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" ::: __clobber_all);
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}
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SEC("socket")
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__description("variable-offset stack write, priv vs unpriv")
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__success
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/* Check that the maximum stack depth is correctly maintained according to the
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* maximum possible variable offset.
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*/
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__log_level(4) __msg("stack depth 16")
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__failure_unpriv
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/* Variable stack access is rejected for unprivileged.
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*/
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__msg_unpriv("R2 variable stack access prohibited for !root")
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__retval(0)
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__naked void stack_write_priv_vs_unpriv(void)
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{
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asm volatile (" \
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/* Get an unknown value */ \
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r2 = *(u32*)(r1 + 0); \
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/* Make it small and 8-byte aligned */ \
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r2 &= 8; \
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r2 -= 16; \
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/* Add it to fp. We now have either fp-8 or \
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* fp-16, but we don't know which \
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*/ \
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r2 += r10; \
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/* Dereference it for a stack write */ \
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r0 = 0; \
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*(u64*)(r2 + 0) = r0; \
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exit; \
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" ::: __clobber_all);
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}
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/* Similar to the previous test, but this time also perform a read from the
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* address written to with a variable offset. The read is allowed, showing that,
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* after a variable-offset write, a priviledged program can read the slots that
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* were in the range of that write (even if the verifier doesn't actually know if
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* the slot being read was really written to or not.
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*
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* Despite this test being mostly a superset, the previous test is also kept for
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* the sake of it checking the stack depth in the case where there is no read.
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*/
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SEC("socket")
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__description("variable-offset stack write followed by read")
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__success
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/* Check that the maximum stack depth is correctly maintained according to the
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* maximum possible variable offset.
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*/
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__log_level(4) __msg("stack depth 16")
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__failure_unpriv
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__msg_unpriv("R2 variable stack access prohibited for !root")
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__retval(0)
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__naked void stack_write_followed_by_read(void)
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{
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asm volatile (" \
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/* Get an unknown value */ \
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r2 = *(u32*)(r1 + 0); \
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/* Make it small and 8-byte aligned */ \
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r2 &= 8; \
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r2 -= 16; \
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/* Add it to fp. We now have either fp-8 or fp-16, but\
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* we don't know which \
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*/ \
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r2 += r10; \
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/* Dereference it for a stack write */ \
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r0 = 0; \
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*(u64*)(r2 + 0) = r0; \
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/* Now read from the address we just wrote. */ \
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r3 = *(u64*)(r2 + 0); \
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r0 = 0; \
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exit; \
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" ::: __clobber_all);
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}
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SEC("socket")
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__description("variable-offset stack write clobbers spilled regs")
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__failure
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/* In the priviledged case, dereferencing a spilled-and-then-filled
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* register is rejected because the previous variable offset stack
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* write might have overwritten the spilled pointer (i.e. we lose track
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* of the spilled register when we analyze the write).
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*/
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__msg("R2 invalid mem access 'scalar'")
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__failure_unpriv
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/* The unprivileged case is not too interesting; variable
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* stack access is rejected.
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*/
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__msg_unpriv("R2 variable stack access prohibited for !root")
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__naked void stack_write_clobbers_spilled_regs(void)
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{
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asm volatile (" \
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/* Dummy instruction; needed because we need to patch the next one\
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* and we can't patch the first instruction. \
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*/ \
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r6 = 0; \
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/* Make R0 a map ptr */ \
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r0 = %[map_hash_8b] ll; \
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/* Get an unknown value */ \
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r2 = *(u32*)(r1 + 0); \
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/* Make it small and 8-byte aligned */ \
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r2 &= 8; \
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r2 -= 16; \
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/* Add it to fp. We now have either fp-8 or fp-16, but\
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* we don't know which. \
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*/ \
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r2 += r10; \
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/* Spill R0(map ptr) into stack */ \
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*(u64*)(r10 - 8) = r0; \
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/* Dereference the unknown value for a stack write */\
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r0 = 0; \
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*(u64*)(r2 + 0) = r0; \
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/* Fill the register back into R2 */ \
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r2 = *(u64*)(r10 - 8); \
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/* Try to dereference R2 for a memory load */ \
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r0 = *(u64*)(r2 + 8); \
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exit; \
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" :
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: __imm_addr(map_hash_8b)
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: __clobber_all);
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}
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SEC("sockops")
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__description("indirect variable-offset stack access, unbounded")
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__failure __msg("invalid unbounded variable-offset indirect access to stack R4")
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__naked void variable_offset_stack_access_unbounded(void)
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{
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asm volatile (" \
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r2 = 6; \
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r3 = 28; \
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/* Fill the top 16 bytes of the stack. */ \
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r4 = 0; \
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*(u64*)(r10 - 16) = r4; \
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r4 = 0; \
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*(u64*)(r10 - 8) = r4; \
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/* Get an unknown value. */ \
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r4 = *(u64*)(r1 + %[bpf_sock_ops_bytes_received]);\
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/* Check the lower bound but don't check the upper one. */\
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if r4 s< 0 goto l0_%=; \
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/* Point the lower bound to initialized stack. Offset is now in range\
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* from fp-16 to fp+0x7fffffffffffffef, i.e. max value is unbounded.\
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*/ \
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r4 -= 16; \
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r4 += r10; \
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r5 = 8; \
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/* Dereference it indirectly. */ \
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call %[bpf_getsockopt]; \
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l0_%=: r0 = 0; \
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exit; \
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" :
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: __imm(bpf_getsockopt),
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__imm_const(bpf_sock_ops_bytes_received, offsetof(struct bpf_sock_ops, bytes_received))
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: __clobber_all);
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}
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SEC("lwt_in")
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__description("indirect variable-offset stack access, max out of bound")
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__failure __msg("invalid variable-offset indirect access to stack R2")
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__naked void access_max_out_of_bound(void)
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{
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asm volatile (" \
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/* Fill the top 8 bytes of the stack */ \
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r2 = 0; \
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*(u64*)(r10 - 8) = r2; \
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/* Get an unknown value */ \
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r2 = *(u32*)(r1 + 0); \
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/* Make it small and 4-byte aligned */ \
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r2 &= 4; \
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r2 -= 8; \
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/* add it to fp. We now have either fp-4 or fp-8, but\
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* we don't know which \
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*/ \
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r2 += r10; \
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/* dereference it indirectly */ \
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r1 = %[map_hash_8b] ll; \
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call %[bpf_map_lookup_elem]; \
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r0 = 0; \
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exit; \
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" :
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: __imm(bpf_map_lookup_elem),
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__imm_addr(map_hash_8b)
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: __clobber_all);
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}
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/* Similar to the test above, but this time check the special case of a
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* zero-sized stack access. We used to have a bug causing crashes for zero-sized
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* out-of-bounds accesses.
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*/
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SEC("socket")
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__description("indirect variable-offset stack access, zero-sized, max out of bound")
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__failure __msg("invalid variable-offset indirect access to stack R1")
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__naked void zero_sized_access_max_out_of_bound(void)
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{
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asm volatile (" \
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r0 = 0; \
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/* Fill some stack */ \
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*(u64*)(r10 - 16) = r0; \
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*(u64*)(r10 - 8) = r0; \
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/* Get an unknown value */ \
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r1 = *(u32*)(r1 + 0); \
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r1 &= 63; \
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r1 += -16; \
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/* r1 is now anywhere in [-16,48) */ \
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r1 += r10; \
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r2 = 0; \
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r3 = 0; \
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call %[bpf_probe_read_kernel]; \
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exit; \
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" :
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: __imm(bpf_probe_read_kernel)
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: __clobber_all);
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}
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SEC("lwt_in")
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__description("indirect variable-offset stack access, min out of bound")
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__failure __msg("invalid variable-offset indirect access to stack R2")
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__naked void access_min_out_of_bound(void)
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{
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asm volatile (" \
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/* Fill the top 8 bytes of the stack */ \
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r2 = 0; \
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*(u64*)(r10 - 8) = r2; \
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/* Get an unknown value */ \
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r2 = *(u32*)(r1 + 0); \
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/* Make it small and 4-byte aligned */ \
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r2 &= 4; \
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r2 -= 516; \
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/* add it to fp. We now have either fp-516 or fp-512, but\
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* we don't know which \
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*/ \
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r2 += r10; \
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/* dereference it indirectly */ \
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r1 = %[map_hash_8b] ll; \
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call %[bpf_map_lookup_elem]; \
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r0 = 0; \
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exit; \
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" :
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: __imm(bpf_map_lookup_elem),
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__imm_addr(map_hash_8b)
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: __clobber_all);
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}
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SEC("cgroup/skb")
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__description("indirect variable-offset stack access, min_off < min_initialized")
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__success
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__failure_unpriv __msg_unpriv("R2 variable stack access prohibited for !root")
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__naked void access_min_off_min_initialized(void)
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{
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asm volatile (" \
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/* Fill only the top 8 bytes of the stack. */ \
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r2 = 0; \
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*(u64*)(r10 - 8) = r2; \
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/* Get an unknown value */ \
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r2 = *(u32*)(r1 + 0); \
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/* Make it small and 4-byte aligned. */ \
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r2 &= 4; \
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r2 -= 16; \
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/* Add it to fp. We now have either fp-12 or fp-16, but we don't know\
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* which. fp-16 size 8 is partially uninitialized stack.\
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*/ \
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r2 += r10; \
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/* Dereference it indirectly. */ \
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r1 = %[map_hash_8b] ll; \
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call %[bpf_map_lookup_elem]; \
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r0 = 0; \
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exit; \
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" :
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: __imm(bpf_map_lookup_elem),
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__imm_addr(map_hash_8b)
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: __clobber_all);
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}
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SEC("cgroup/skb")
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__description("indirect variable-offset stack access, priv vs unpriv")
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__success __failure_unpriv
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__msg_unpriv("R2 variable stack access prohibited for !root")
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__retval(0)
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__naked void stack_access_priv_vs_unpriv(void)
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{
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asm volatile (" \
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/* Fill the top 16 bytes of the stack. */ \
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r2 = 0; \
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*(u64*)(r10 - 16) = r2; \
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r2 = 0; \
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*(u64*)(r10 - 8) = r2; \
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/* Get an unknown value. */ \
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r2 = *(u32*)(r1 + 0); \
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/* Make it small and 4-byte aligned. */ \
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r2 &= 4; \
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r2 -= 16; \
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/* Add it to fp. We now have either fp-12 or fp-16, we don't know\
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* which, but either way it points to initialized stack.\
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*/ \
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r2 += r10; \
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/* Dereference it indirectly. */ \
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r1 = %[map_hash_8b] ll; \
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call %[bpf_map_lookup_elem]; \
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r0 = 0; \
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exit; \
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" :
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: __imm(bpf_map_lookup_elem),
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__imm_addr(map_hash_8b)
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: __clobber_all);
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}
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SEC("lwt_in")
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__description("indirect variable-offset stack access, ok")
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__success __retval(0)
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__naked void variable_offset_stack_access_ok(void)
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{
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asm volatile (" \
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/* Fill the top 16 bytes of the stack. */ \
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r2 = 0; \
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*(u64*)(r10 - 16) = r2; \
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r2 = 0; \
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*(u64*)(r10 - 8) = r2; \
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/* Get an unknown value. */ \
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r2 = *(u32*)(r1 + 0); \
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/* Make it small and 4-byte aligned. */ \
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r2 &= 4; \
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r2 -= 16; \
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/* Add it to fp. We now have either fp-12 or fp-16, we don't know\
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* which, but either way it points to initialized stack.\
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*/ \
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r2 += r10; \
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/* Dereference it indirectly. */ \
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r1 = %[map_hash_8b] ll; \
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call %[bpf_map_lookup_elem]; \
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r0 = 0; \
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exit; \
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" :
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: __imm(bpf_map_lookup_elem),
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__imm_addr(map_hash_8b)
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: __clobber_all);
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}
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char _license[] SEC("license") = "GPL";
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