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selftests/bpf: add precision propagation tests in the presence of subprogs

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Add a bunch of tests validating verifier's precision backpropagation
logic in the presence of subprog calls and/or callback-calling
helpers/kfuncs.

We validate the following conditions:
  - subprog_result_precise: static subprog r0 result precision handling;
  - global_subprog_result_precise: global subprog r0 precision
    shortcutting, similar to BPF helper handling;
  - callback_result_precise: similarly r0 marking precise for
    callback-calling helpers;
  - parent_callee_saved_reg_precise, parent_callee_saved_reg_precise_global:
    propagation of precision for callee-saved registers bypassing
    static/global subprogs;
  - parent_callee_saved_reg_precise_with_callback: same as above, but in
    the presence of callback-calling helper;
  - parent_stack_slot_precise, parent_stack_slot_precise_global:
    similar to above, but instead propagating precision of stack slot
    (spilled SCALAR reg);
  - parent_stack_slot_precise_with_callback: same as above, but in the
    presence of callback-calling helper;
  - subprog_arg_precise: propagation of precision of static subprog's
    input argument back to caller;
  - subprog_spill_into_parent_stack_slot_precise: negative test
    validating that verifier currently can't support backtracking of stack
    access with non-r10 register, we validate that we fallback to
    forcing precision for all SCALARs.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230505043317.3629845-10-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2023-05-04 21:33:16 -07:00 committed by Alexei Starovoitov
parent fde2a3882b
commit 3ef3d2177b
3 changed files with 542 additions and 0 deletions
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2
tools/testing/selftests/bpf/prog_tests/verifier.c
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@ -55,6 +55,7 @@
#include "verifier_spill_fill.skel.h"
#include "verifier_spin_lock.skel.h"
#include "verifier_stack_ptr.skel.h"
#include "verifier_subprog_precision.skel.h"
#include "verifier_subreg.skel.h"
#include "verifier_uninit.skel.h"
#include "verifier_unpriv.skel.h"
@ -154,6 +155,7 @@ void test_verifier_sock(void) { RUN(verifier_sock); }
void test_verifier_spill_fill(void) { RUN(verifier_spill_fill); }
void test_verifier_spin_lock(void) { RUN(verifier_spin_lock); }
void test_verifier_stack_ptr(void) { RUN(verifier_stack_ptr); }
void test_verifier_subprog_precision(void) { RUN(verifier_subprog_precision); }
void test_verifier_subreg(void) { RUN(verifier_subreg); }
void test_verifier_uninit(void) { RUN(verifier_uninit); }
void test_verifier_unpriv(void) { RUN(verifier_unpriv); }

4
tools/testing/selftests/bpf/progs/bpf_misc.h
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@ -86,6 +86,10 @@
#define POINTER_VALUE 0xcafe4all
#define TEST_DATA_LEN 64
#ifndef __used
#define __used __attribute__((used))
#endif
#if defined(__TARGET_ARCH_x86)
#define SYSCALL_WRAPPER 1
#define SYS_PREFIX "__x64_"

536
tools/testing/selftests/bpf/progs/verifier_subprog_precision.c Normal file
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@ -0,0 +1,536 @@
// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
#include <errno.h>
#include <string.h>
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include "bpf_misc.h"
#define ARRAY_SIZE(x) (sizeof(x) / sizeof(x[0]))
int vals[] SEC(".data.vals") = {1, 2, 3, 4};
__naked __noinline __used
static unsigned long identity_subprog()
{
/* the simplest *static* 64-bit identity function */
asm volatile (
"r0 = r1;"
"exit;"
);
}
__noinline __used
unsigned long global_identity_subprog(__u64 x)
{
/* the simplest *global* 64-bit identity function */
return x;
}
__naked __noinline __used
static unsigned long callback_subprog()
{
/* the simplest callback function */
asm volatile (
"r0 = 0;"
"exit;"
);
}
SEC("?raw_tp")
__success __log_level(2)
__msg("7: (0f) r1 += r0")
__msg("mark_precise: frame0: regs=r0 stack= before 6: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r0 stack= before 5: (27) r0 *= 4")
__msg("mark_precise: frame0: regs=r0 stack= before 11: (95) exit")
__msg("mark_precise: frame1: regs=r0 stack= before 10: (bf) r0 = r1")
__msg("mark_precise: frame1: regs=r1 stack= before 4: (85) call pc+5")
__msg("mark_precise: frame0: regs=r1 stack= before 3: (bf) r1 = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 3")
__naked int subprog_result_precise(void)
{
asm volatile (
"r6 = 3;"
/* pass r6 through r1 into subprog to get it back as r0;
* this whole chain will have to be marked as precise later
*/
"r1 = r6;"
"call identity_subprog;"
/* now use subprog's returned value (which is a
* r6 -> r1 -> r0 chain), as index into vals array, forcing
* all of that to be known precisely
*/
"r0 *= 4;"
"r1 = %[vals];"
/* here r0->r1->r6 chain is forced to be precise and has to be
* propagated back to the beginning, including through the
* subprog call
*/
"r1 += r0;"
"r0 = *(u32 *)(r1 + 0);"
"exit;"
:
: __imm_ptr(vals)
: __clobber_common, "r6"
);
}
SEC("?raw_tp")
__success __log_level(2)
__msg("9: (0f) r1 += r0")
__msg("mark_precise: frame0: last_idx 9 first_idx 0")
__msg("mark_precise: frame0: regs=r0 stack= before 8: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r0 stack= before 7: (27) r0 *= 4")
__msg("mark_precise: frame0: regs=r0 stack= before 5: (a5) if r0 < 0x4 goto pc+1")
__msg("mark_precise: frame0: regs=r0 stack= before 4: (85) call pc+7")
__naked int global_subprog_result_precise(void)
{
asm volatile (
"r6 = 3;"
/* pass r6 through r1 into subprog to get it back as r0;
* given global_identity_subprog is global, precision won't
* propagate all the way back to r6
*/
"r1 = r6;"
"call global_identity_subprog;"
/* now use subprog's returned value (which is unknown now, so
* we need to clamp it), as index into vals array, forcing r0
* to be marked precise (with no effect on r6, though)
*/
"if r0 < %[vals_arr_sz] goto 1f;"
"r0 = %[vals_arr_sz] - 1;"
"1:"
"r0 *= 4;"
"r1 = %[vals];"
/* here r0 is forced to be precise and has to be
* propagated back to the global subprog call, but it
* shouldn't go all the way to mark r6 as precise
*/
"r1 += r0;"
"r0 = *(u32 *)(r1 + 0);"
"exit;"
:
: __imm_ptr(vals),
__imm_const(vals_arr_sz, ARRAY_SIZE(vals))
: __clobber_common, "r6"
);
}
SEC("?raw_tp")
__success __log_level(2)
__msg("14: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 14 first_idx 10")
__msg("mark_precise: frame0: regs=r6 stack= before 13: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 12: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 11: (25) if r6 > 0x3 goto pc+4")
__msg("mark_precise: frame0: regs=r6 stack= before 10: (bf) r6 = r0")
__msg("mark_precise: frame0: parent state regs=r0 stack=:")
__msg("mark_precise: frame0: last_idx 18 first_idx 0")
__msg("mark_precise: frame0: regs=r0 stack= before 18: (95) exit")
__naked int callback_result_precise(void)
{
asm volatile (
"r6 = 3;"
/* call subprog and use result; r0 shouldn't propagate back to
* callback_subprog
*/
"r1 = r6;" /* nr_loops */
"r2 = %[callback_subprog];" /* callback_fn */
"r3 = 0;" /* callback_ctx */
"r4 = 0;" /* flags */
"call %[bpf_loop];"
"r6 = r0;"
"if r6 > 3 goto 1f;"
"r6 *= 4;"
"r1 = %[vals];"
/* here r6 is forced to be precise and has to be propagated
* back to the bpf_loop() call, but not beyond
*/
"r1 += r6;"
"r0 = *(u32 *)(r1 + 0);"
"1:"
"exit;"
:
: __imm_ptr(vals),
__imm_ptr(callback_subprog),
__imm(bpf_loop)
: __clobber_common, "r6"
);
}
SEC("?raw_tp")
__success __log_level(2)
__msg("7: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 7 first_idx 0")
__msg("mark_precise: frame0: regs=r6 stack= before 6: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 5: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 11: (95) exit")
__msg("mark_precise: frame1: regs= stack= before 10: (bf) r0 = r1")
__msg("mark_precise: frame1: regs= stack= before 4: (85) call pc+5")
__msg("mark_precise: frame0: regs=r6 stack= before 3: (b7) r1 = 0")
__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 3")
__naked int parent_callee_saved_reg_precise(void)
{
asm volatile (
"r6 = 3;"
/* call subprog and ignore result; we need this call only to
* complicate jump history
*/
"r1 = 0;"
"call identity_subprog;"
"r6 *= 4;"
"r1 = %[vals];"
/* here r6 is forced to be precise and has to be propagated
* back to the beginning, handling (and ignoring) subprog call
*/
"r1 += r6;"
"r0 = *(u32 *)(r1 + 0);"
"exit;"
:
: __imm_ptr(vals)
: __clobber_common, "r6"
);
}
SEC("?raw_tp")
__success __log_level(2)
__msg("7: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 7 first_idx 0")
__msg("mark_precise: frame0: regs=r6 stack= before 6: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 5: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 4: (85) call pc+5")
__msg("mark_precise: frame0: regs=r6 stack= before 3: (b7) r1 = 0")
__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 3")
__naked int parent_callee_saved_reg_precise_global(void)
{
asm volatile (
"r6 = 3;"
/* call subprog and ignore result; we need this call only to
* complicate jump history
*/
"r1 = 0;"
"call global_identity_subprog;"
"r6 *= 4;"
"r1 = %[vals];"
/* here r6 is forced to be precise and has to be propagated
* back to the beginning, handling (and ignoring) subprog call
*/
"r1 += r6;"
"r0 = *(u32 *)(r1 + 0);"
"exit;"
:
: __imm_ptr(vals)
: __clobber_common, "r6"
);
}
SEC("?raw_tp")
__success __log_level(2)
__msg("12: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 12 first_idx 10")
__msg("mark_precise: frame0: regs=r6 stack= before 11: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 10: (27) r6 *= 4")
__msg("mark_precise: frame0: parent state regs=r6 stack=:")
__msg("mark_precise: frame0: last_idx 16 first_idx 0")
__msg("mark_precise: frame0: regs=r6 stack= before 16: (95) exit")
__msg("mark_precise: frame1: regs= stack= before 15: (b7) r0 = 0")
__msg("mark_precise: frame1: regs= stack= before 9: (85) call bpf_loop#181")
__msg("mark_precise: frame0: regs=r6 stack= before 8: (b7) r4 = 0")
__msg("mark_precise: frame0: regs=r6 stack= before 7: (b7) r3 = 0")
__msg("mark_precise: frame0: regs=r6 stack= before 6: (bf) r2 = r8")
__msg("mark_precise: frame0: regs=r6 stack= before 5: (b7) r1 = 1")
__msg("mark_precise: frame0: regs=r6 stack= before 4: (b7) r6 = 3")
__naked int parent_callee_saved_reg_precise_with_callback(void)
{
asm volatile (
"r6 = 3;"
/* call subprog and ignore result; we need this call only to
* complicate jump history
*/
"r1 = 1;" /* nr_loops */
"r2 = %[callback_subprog];" /* callback_fn */
"r3 = 0;" /* callback_ctx */
"r4 = 0;" /* flags */
"call %[bpf_loop];"
"r6 *= 4;"
"r1 = %[vals];"
/* here r6 is forced to be precise and has to be propagated
* back to the beginning, handling (and ignoring) callback call
*/
"r1 += r6;"
"r0 = *(u32 *)(r1 + 0);"
"exit;"
:
: __imm_ptr(vals),
__imm_ptr(callback_subprog),
__imm(bpf_loop)
: __clobber_common, "r6"
);
}
SEC("?raw_tp")
__success __log_level(2)
__msg("9: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 9 first_idx 6")
__msg("mark_precise: frame0: regs=r6 stack= before 8: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 7: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 6: (79) r6 = *(u64 *)(r10 -8)")
__msg("mark_precise: frame0: parent state regs= stack=-8:")
__msg("mark_precise: frame0: last_idx 13 first_idx 0")
__msg("mark_precise: frame0: regs= stack=-8 before 13: (95) exit")
__msg("mark_precise: frame1: regs= stack= before 12: (bf) r0 = r1")
__msg("mark_precise: frame1: regs= stack= before 5: (85) call pc+6")
__msg("mark_precise: frame0: regs= stack=-8 before 4: (b7) r1 = 0")
__msg("mark_precise: frame0: regs= stack=-8 before 3: (7b) *(u64 *)(r10 -8) = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 3")
__naked int parent_stack_slot_precise(void)
{
asm volatile (
/* spill reg */
"r6 = 3;"
"*(u64 *)(r10 - 8) = r6;"
/* call subprog and ignore result; we need this call only to
* complicate jump history
*/
"r1 = 0;"
"call identity_subprog;"
/* restore reg from stack; in this case we'll be carrying
* stack mask when going back into subprog through jump
* history
*/
"r6 = *(u64 *)(r10 - 8);"
"r6 *= 4;"
"r1 = %[vals];"
/* here r6 is forced to be precise and has to be propagated
* back to the beginning, handling (and ignoring) subprog call
*/
"r1 += r6;"
"r0 = *(u32 *)(r1 + 0);"
"exit;"
:
: __imm_ptr(vals)
: __clobber_common, "r6"
);
}
SEC("?raw_tp")
__success __log_level(2)
__msg("9: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 9 first_idx 6")
__msg("mark_precise: frame0: regs=r6 stack= before 8: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 7: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 6: (79) r6 = *(u64 *)(r10 -8)")
__msg("mark_precise: frame0: parent state regs= stack=-8:")
__msg("mark_precise: frame0: last_idx 5 first_idx 0")
__msg("mark_precise: frame0: regs= stack=-8 before 5: (85) call pc+6")
__msg("mark_precise: frame0: regs= stack=-8 before 4: (b7) r1 = 0")
__msg("mark_precise: frame0: regs= stack=-8 before 3: (7b) *(u64 *)(r10 -8) = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 3")
__naked int parent_stack_slot_precise_global(void)
{
asm volatile (
/* spill reg */
"r6 = 3;"
"*(u64 *)(r10 - 8) = r6;"
/* call subprog and ignore result; we need this call only to
* complicate jump history
*/
"r1 = 0;"
"call global_identity_subprog;"
/* restore reg from stack; in this case we'll be carrying
* stack mask when going back into subprog through jump
* history
*/
"r6 = *(u64 *)(r10 - 8);"
"r6 *= 4;"
"r1 = %[vals];"
/* here r6 is forced to be precise and has to be propagated
* back to the beginning, handling (and ignoring) subprog call
*/
"r1 += r6;"
"r0 = *(u32 *)(r1 + 0);"
"exit;"
:
: __imm_ptr(vals)
: __clobber_common, "r6"
);
}
SEC("?raw_tp")
__success __log_level(2)
__msg("14: (0f) r1 += r6")
__msg("mark_precise: frame0: last_idx 14 first_idx 11")
__msg("mark_precise: frame0: regs=r6 stack= before 13: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r6 stack= before 12: (27) r6 *= 4")
__msg("mark_precise: frame0: regs=r6 stack= before 11: (79) r6 = *(u64 *)(r10 -8)")
__msg("mark_precise: frame0: parent state regs= stack=-8:")
__msg("mark_precise: frame0: last_idx 18 first_idx 0")
__msg("mark_precise: frame0: regs= stack=-8 before 18: (95) exit")
__msg("mark_precise: frame1: regs= stack= before 17: (b7) r0 = 0")
__msg("mark_precise: frame1: regs= stack= before 10: (85) call bpf_loop#181")
__msg("mark_precise: frame0: regs= stack=-8 before 9: (b7) r4 = 0")
__msg("mark_precise: frame0: regs= stack=-8 before 8: (b7) r3 = 0")
__msg("mark_precise: frame0: regs= stack=-8 before 7: (bf) r2 = r8")
__msg("mark_precise: frame0: regs= stack=-8 before 6: (bf) r1 = r6")
__msg("mark_precise: frame0: regs= stack=-8 before 5: (7b) *(u64 *)(r10 -8) = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 4: (b7) r6 = 3")
__naked int parent_stack_slot_precise_with_callback(void)
{
asm volatile (
/* spill reg */
"r6 = 3;"
"*(u64 *)(r10 - 8) = r6;"
/* ensure we have callback frame in jump history */
"r1 = r6;" /* nr_loops */
"r2 = %[callback_subprog];" /* callback_fn */
"r3 = 0;" /* callback_ctx */
"r4 = 0;" /* flags */
"call %[bpf_loop];"
/* restore reg from stack; in this case we'll be carrying
* stack mask when going back into subprog through jump
* history
*/
"r6 = *(u64 *)(r10 - 8);"
"r6 *= 4;"
"r1 = %[vals];"
/* here r6 is forced to be precise and has to be propagated
* back to the beginning, handling (and ignoring) subprog call
*/
"r1 += r6;"
"r0 = *(u32 *)(r1 + 0);"
"exit;"
:
: __imm_ptr(vals),
__imm_ptr(callback_subprog),
__imm(bpf_loop)
: __clobber_common, "r6"
);
}
__noinline __used
static __u64 subprog_with_precise_arg(__u64 x)
{
return vals[x]; /* x is forced to be precise */
}
SEC("?raw_tp")
__success __log_level(2)
__msg("8: (0f) r2 += r1")
__msg("mark_precise: frame1: last_idx 8 first_idx 0")
__msg("mark_precise: frame1: regs=r1 stack= before 6: (18) r2 = ")
__msg("mark_precise: frame1: regs=r1 stack= before 5: (67) r1 <<= 2")
__msg("mark_precise: frame1: regs=r1 stack= before 2: (85) call pc+2")
__msg("mark_precise: frame0: regs=r1 stack= before 1: (bf) r1 = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 0: (b7) r6 = 3")
__naked int subprog_arg_precise(void)
{
asm volatile (
"r6 = 3;"
"r1 = r6;"
/* subprog_with_precise_arg expects its argument to be
* precise, so r1->r6 will be marked precise from inside the
* subprog
*/
"call subprog_with_precise_arg;"
"r0 += r6;"
"exit;"
:
:
: __clobber_common, "r6"
);
}
/* r1 is pointer to stack slot;
* r2 is a register to spill into that slot
* subprog also spills r2 into its own stack slot
*/
__naked __noinline __used
static __u64 subprog_spill_reg_precise(void)
{
asm volatile (
/* spill to parent stack */
"*(u64 *)(r1 + 0) = r2;"
/* spill to subprog stack (we use -16 offset to avoid
* accidental confusion with parent's -8 stack slot in
* verifier log output)
*/
"*(u64 *)(r10 - 16) = r2;"
/* use both spills as return result to propagete precision everywhere */
"r0 = *(u64 *)(r10 - 16);"
"r2 = *(u64 *)(r1 + 0);"
"r0 += r2;"
"exit;"
);
}
SEC("?raw_tp")
__success __log_level(2)
/* precision backtracking can't currently handle stack access not through r10,
* so we won't be able to mark stack slot fp-8 as precise, and so will
* fallback to forcing all as precise
*/
__msg("mark_precise: frame0: falling back to forcing all scalars precise")
__naked int subprog_spill_into_parent_stack_slot_precise(void)
{
asm volatile (
"r6 = 1;"
/* pass pointer to stack slot and r6 to subprog;
* r6 will be marked precise and spilled into fp-8 slot, which
* also should be marked precise
*/
"r1 = r10;"
"r1 += -8;"
"r2 = r6;"
"call subprog_spill_reg_precise;"
/* restore reg from stack; in this case we'll be carrying
* stack mask when going back into subprog through jump
* history
*/
"r7 = *(u64 *)(r10 - 8);"
"r7 *= 4;"
"r1 = %[vals];"
/* here r7 is forced to be precise and has to be propagated
* back to the beginning, handling subprog call and logic
*/
"r1 += r7;"
"r0 = *(u32 *)(r1 + 0);"
"exit;"
:
: __imm_ptr(vals)
: __clobber_common, "r6", "r7"
);
}
__naked __noinline __used
static __u64 subprog_with_checkpoint(void)
{
asm volatile (
"r0 = 0;"
/* guaranteed checkpoint if BPF_F_TEST_STATE_FREQ is used */
"goto +0;"
"exit;"
);
}
char _license[] SEC("license") = "GPL";