6.6-stable review patch. If anyone has any objections, please let me know.
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From: Tao Lyu tao.lyu@epfl.ch
[ Upstream commit b0e66977dc072906bb76555fb1a64261d7f63d0f ]
When CAP_PERFMON and CAP_SYS_ADMIN (allow_ptr_leaks) are disabled, the verifier aims to reject partial overwrite on an 8-byte stack slot that contains a spilled pointer.
However, in such a scenario, it rejects all partial stack overwrites as long as the targeted stack slot is a spilled register, because it does not check if the stack slot is a spilled pointer.
Incomplete checks will result in the rejection of valid programs, which spill narrower scalar values onto scalar slots, as shown below.
0: R1=ctx() R10=fp0 ; asm volatile ( @ repro.bpf.c:679 0: (7a) *(u64 *)(r10 -8) = 1 ; R10=fp0 fp-8_w=1 1: (62) *(u32 *)(r10 -8) = 1 attempt to corrupt spilled pointer on stack processed 2 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0.
Fix this by expanding the check to not consider spilled scalar registers when rejecting the write into the stack.
Previous discussion on this patch is at link [0].
[0]: https://lore.kernel.org/bpf/20240403202409.2615469-1-tao.lyu@epfl.ch
Fixes: ab125ed3ec1c ("bpf: fix check for attempt to corrupt spilled pointer") Acked-by: Eduard Zingerman eddyz87@gmail.com Acked-by: Andrii Nakryiko andrii@kernel.org Signed-off-by: Tao Lyu tao.lyu@epfl.ch Signed-off-by: Kumar Kartikeya Dwivedi memxor@gmail.com Link: https://lore.kernel.org/r/20241204044757.1483141-3-memxor@gmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 5ca02af3a8728..3f47cfa17141a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4599,6 +4599,7 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env, */ if (!env->allow_ptr_leaks && is_spilled_reg(&state->stack[spi]) && + !is_spilled_scalar_reg(&state->stack[spi]) && size != BPF_REG_SIZE) { verbose(env, "attempt to corrupt spilled pointer on stack\n"); return -EACCES;