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selftests/bpf: States pruning checks for scalar vs STACK_MISC

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Check that stacksafe() compares spilled scalars with STACK_MISC.
The following combinations are explored:
- old spill of imprecise scalar is equivalent to cur STACK_{MISC,INVALID}
  (plus error in unpriv mode);
- old spill of precise scalar is not equivalent to cur STACK_MISC;
- old STACK_MISC is equivalent to cur scalar;
- old STACK_MISC is not equivalent to cur non-scalar.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240127175237.526726-7-maxtram95@gmail.com
This commit is contained in:
Eduard Zingerman 2024-01-27 19:52:37 +02:00 committed by Andrii Nakryiko
parent 6efbde200b
commit 73a28d9d00
1 changed files with 154 additions and 0 deletions
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154
tools/testing/selftests/bpf/progs/verifier_spill_fill.c
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@ -1090,4 +1090,158 @@ l0_%=: r1 >>= 32; \
: __clobber_all);
}
/* stacksafe(): check if stack spill of an imprecise scalar in old state
* is considered equivalent to STACK_{MISC,INVALID} in cur state.
*/
SEC("socket")
__success __log_level(2)
__msg("8: (79) r1 = *(u64 *)(r10 -8)")
__msg("8: safe")
__msg("processed 11 insns")
/* STACK_INVALID should prevent verifier in unpriv mode from
* considering states equivalent and force an error on second
* verification path (entry - label 1 - label 2).
*/
__failure_unpriv
__msg_unpriv("8: (79) r1 = *(u64 *)(r10 -8)")
__msg_unpriv("9: (95) exit")
__msg_unpriv("8: (79) r1 = *(u64 *)(r10 -8)")
__msg_unpriv("invalid read from stack off -8+2 size 8")
__flag(BPF_F_TEST_STATE_FREQ)
__naked void old_imprecise_scalar_vs_cur_stack_misc(void)
{
asm volatile(
/* get a random value for branching */
"call %[bpf_ktime_get_ns];"
"if r0 == 0 goto 1f;"
/* conjure scalar at fp-8 */
"r0 = 42;"
"*(u64*)(r10 - 8) = r0;"
"goto 2f;"
"1:"
/* conjure STACK_{MISC,INVALID} at fp-8 */
"call %[bpf_ktime_get_ns];"
"*(u16*)(r10 - 8) = r0;"
"*(u16*)(r10 - 4) = r0;"
"2:"
/* read fp-8, should be considered safe on second visit */
"r1 = *(u64*)(r10 - 8);"
"exit;"
:
: __imm(bpf_ktime_get_ns)
: __clobber_all);
}
/* stacksafe(): check that stack spill of a precise scalar in old state
* is not considered equivalent to STACK_MISC in cur state.
*/
SEC("socket")
__success __log_level(2)
/* verifier should visit 'if r1 == 0x2a ...' two times:
* - once for path entry - label 2;
* - once for path entry - label 1 - label 2.
*/
__msg("if r1 == 0x2a goto pc+0")
__msg("if r1 == 0x2a goto pc+0")
__msg("processed 15 insns")
__flag(BPF_F_TEST_STATE_FREQ)
__naked void old_precise_scalar_vs_cur_stack_misc(void)
{
asm volatile(
/* get a random value for branching */
"call %[bpf_ktime_get_ns];"
"if r0 == 0 goto 1f;"
/* conjure scalar at fp-8 */
"r0 = 42;"
"*(u64*)(r10 - 8) = r0;"
"goto 2f;"
"1:"
/* conjure STACK_MISC at fp-8 */
"call %[bpf_ktime_get_ns];"
"*(u64*)(r10 - 8) = r0;"
"*(u32*)(r10 - 4) = r0;"
"2:"
/* read fp-8, should not be considered safe on second visit */
"r1 = *(u64*)(r10 - 8);"
/* use r1 in precise context */
"if r1 == 42 goto +0;"
"exit;"
:
: __imm(bpf_ktime_get_ns)
: __clobber_all);
}
/* stacksafe(): check if STACK_MISC in old state is considered
* equivalent to stack spill of a scalar in cur state.
*/
SEC("socket")
__success __log_level(2)
__msg("8: (79) r0 = *(u64 *)(r10 -8)")
__msg("8: safe")
__msg("processed 11 insns")
__flag(BPF_F_TEST_STATE_FREQ)
__naked void old_stack_misc_vs_cur_scalar(void)
{
asm volatile(
/* get a random value for branching */
"call %[bpf_ktime_get_ns];"
"if r0 == 0 goto 1f;"
/* conjure STACK_{MISC,INVALID} at fp-8 */
"call %[bpf_ktime_get_ns];"
"*(u16*)(r10 - 8) = r0;"
"*(u16*)(r10 - 4) = r0;"
"goto 2f;"
"1:"
/* conjure scalar at fp-8 */
"r0 = 42;"
"*(u64*)(r10 - 8) = r0;"
"2:"
/* read fp-8, should be considered safe on second visit */
"r0 = *(u64*)(r10 - 8);"
"exit;"
:
: __imm(bpf_ktime_get_ns)
: __clobber_all);
}
/* stacksafe(): check that STACK_MISC in old state is not considered
* equivalent to stack spill of a non-scalar in cur state.
*/
SEC("socket")
__success __log_level(2)
/* verifier should process exit instructions twice:
* - once for path entry - label 2;
* - once for path entry - label 1 - label 2.
*/
__msg("r1 = *(u64 *)(r10 -8)")
__msg("exit")
__msg("r1 = *(u64 *)(r10 -8)")
__msg("exit")
__msg("processed 11 insns")
__flag(BPF_F_TEST_STATE_FREQ)
__naked void old_stack_misc_vs_cur_ctx_ptr(void)
{
asm volatile(
/* remember context pointer in r9 */
"r9 = r1;"
/* get a random value for branching */
"call %[bpf_ktime_get_ns];"
"if r0 == 0 goto 1f;"
/* conjure STACK_MISC at fp-8 */
"call %[bpf_ktime_get_ns];"
"*(u64*)(r10 - 8) = r0;"
"*(u32*)(r10 - 4) = r0;"
"goto 2f;"
"1:"
/* conjure context pointer in fp-8 */
"*(u64*)(r10 - 8) = r9;"
"2:"
/* read fp-8, should not be considered safe on second visit */
"r1 = *(u64*)(r10 - 8);"
"exit;"
:
: __imm(bpf_ktime_get_ns)
: __clobber_all);
}
char _license[] SEC("license") = "GPL";