This is a note to let you know that I've just added the patch titled
bpf: Fix narrow scalar spill onto 64-bit spilled scalar slots
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bpf-fix-narrow-scalar-spill-onto-64-bit-spilled-scal.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 56bc7476b3f9340e9dafc6f70bd58743d1d55113
Author: Tao Lyu <tao.lyu@xxxxxxx>
Date: Tue Dec 3 20:47:54 2024 -0800
bpf: Fix narrow scalar spill onto 64-bit spilled scalar slots
[ 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@xxxxxxx
Fixes: ab125ed3ec1c ("bpf: fix check for attempt to corrupt spilled pointer")
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Tao Lyu <tao.lyu@xxxxxxx>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
Link: https://lore.kernel.org/r/20241204044757.1483141-3-memxor@xxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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;
