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selftests/bpf: add stack access precision test

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Add a new selftests that validates precision tracking for stack access
instruction, using both r10-based and non-r10-based accesses. For
non-r10 ones we also make sure to have non-zero var_off to validate that
final stack offset is tracked properly in instruction history
information inside verifier.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231205184248.1502704-3-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2023-12-05 10:42:40 -08:00 committed by Alexei Starovoitov
parent 41f6f64e69
commit 876301881c
1 changed files with 59 additions and 5 deletions
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64
tools/testing/selftests/bpf/progs/verifier_subprog_precision.c
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@ -641,14 +641,68 @@ __naked int subprog_spill_into_parent_stack_slot_precise(void)
);
}
__naked __noinline __used
static __u64 subprog_with_checkpoint(void)
SEC("?raw_tp")
__success __log_level(2)
__msg("17: (0f) r1 += r0")
__msg("mark_precise: frame0: last_idx 17 first_idx 0 subseq_idx -1")
__msg("mark_precise: frame0: regs=r0 stack= before 16: (bf) r1 = r7")
__msg("mark_precise: frame0: regs=r0 stack= before 15: (27) r0 *= 4")
__msg("mark_precise: frame0: regs=r0 stack= before 14: (79) r0 = *(u64 *)(r10 -16)")
__msg("mark_precise: frame0: regs= stack=-16 before 13: (7b) *(u64 *)(r7 -8) = r0")
__msg("mark_precise: frame0: regs=r0 stack= before 12: (79) r0 = *(u64 *)(r8 +16)")
__msg("mark_precise: frame0: regs= stack=-16 before 11: (7b) *(u64 *)(r8 +16) = r0")
__msg("mark_precise: frame0: regs=r0 stack= before 10: (79) r0 = *(u64 *)(r7 -8)")
__msg("mark_precise: frame0: regs= stack=-16 before 9: (7b) *(u64 *)(r10 -16) = r0")
__msg("mark_precise: frame0: regs=r0 stack= before 8: (07) r8 += -32")
__msg("mark_precise: frame0: regs=r0 stack= before 7: (bf) r8 = r10")
__msg("mark_precise: frame0: regs=r0 stack= before 6: (07) r7 += -8")
__msg("mark_precise: frame0: regs=r0 stack= before 5: (bf) r7 = r10")
__msg("mark_precise: frame0: regs=r0 stack= before 21: (95) exit")
__msg("mark_precise: frame1: regs=r0 stack= before 20: (bf) r0 = r1")
__msg("mark_precise: frame1: regs=r1 stack= before 4: (85) call pc+15")
__msg("mark_precise: frame0: regs=r1 stack= before 3: (bf) r1 = r6")
__msg("mark_precise: frame0: regs=r6 stack= before 2: (b7) r6 = 1")
__naked int stack_slot_aliases_precision(void)
{
asm volatile (
"r0 = 0;"
/* guaranteed checkpoint if BPF_F_TEST_STATE_FREQ is used */
"goto +0;"
"r6 = 1;"
/* 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;"
/* let's setup two registers that are aliased to r10 */
"r7 = r10;"
"r7 += -8;" /* r7 = r10 - 8 */
"r8 = r10;"
"r8 += -32;" /* r8 = r10 - 32 */
/* now spill subprog's return value (a r6 -> r1 -> r0 chain)
* a few times through different stack pointer regs, making
* sure to use r10, r7, and r8 both in LDX and STX insns, and
* *importantly* also using a combination of const var_off and
* insn->off to validate that we record final stack slot
* correctly, instead of relying on just insn->off derivation,
* which is only valid for r10-based stack offset
*/
"*(u64 *)(r10 - 16) = r0;"
"r0 = *(u64 *)(r7 - 8);" /* r7 - 8 == r10 - 16 */
"*(u64 *)(r8 + 16) = r0;" /* r8 + 16 = r10 - 16 */
"r0 = *(u64 *)(r8 + 16);"
"*(u64 *)(r7 - 8) = r0;"
"r0 = *(u64 *)(r10 - 16);"
/* get ready to use r0 as an index into array to force precision */
"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 and all the stack spills and loads
*/
"r1 += r0;"
"r0 = *(u32 *)(r1 + 0);"
"exit;"
:
: __imm_ptr(vals)
: __clobber_common, "r6"
);
}