bpf: Fix call offset truncation and OOB read in bpf_patch_call_args()#12025
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kernel-patches-daemon-bpf[bot] wants to merge 3 commits intobpf-next_basefrom
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bpf: Fix call offset truncation and OOB read in bpf_patch_call_args()#12025kernel-patches-daemon-bpf[bot] wants to merge 3 commits intobpf-next_basefrom
kernel-patches-daemon-bpf[bot] wants to merge 3 commits intobpf-next_basefrom
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The interpreters_args array only accommodates stack depths up to MAX_BPF_STACK (512 bytes). However, do_misc_fixups() may allow a larger stack depth if JIT is requested. If JIT compilation later fails and falls back to the interpreter, the verifier invokes bpf_patch_call_args() with this oversized stack depth. This causes a load-time out-of-bounds (OOB) read when calculating the interpreter function pointer index. Fix this by changing bpf_patch_call_args() to return an int and explicitly rejecting the JIT fallback (returning -EINVAL) if the stack depth exceeds MAX_BPF_STACK. Fixes: 1ea47e0 ("bpf: add support for bpf_call to interpreter") Co-developed-by: Tianci Cao <ziye@zju.edu.cn> Signed-off-by: Tianci Cao <ziye@zju.edu.cn> Co-developed-by: Shenghao Yuan <shenghaoyuan0928@163.com> Signed-off-by: Shenghao Yuan <shenghaoyuan0928@163.com> Signed-off-by: Yazhou Tang <tangyazhou518@outlook.com> Acked-by: Xu Kuohai <xukuohai@huawei.com>
Currently, the BPF instruction set allows bpf-to-bpf calls (or internal
calls, pseudo calls) to use a 32-bit imm field to represent the relative
jump offset.
However, when JIT is disabled or falls back to the interpreter, the
verifier invokes bpf_patch_call_args() to rewrite the call instruction.
In this function, the 32-bit imm is downcast to s16 and stored in the off
field.
void bpf_patch_call_args(struct bpf_insn *insn, u32 stack_depth)
{
stack_depth = max_t(u32, stack_depth, 1);
insn->off = (s16) insn->imm;
insn->imm = interpreters_args[(round_up(stack_depth, 32) / 32) - 1] -
__bpf_call_base_args;
insn->code = BPF_JMP | BPF_CALL_ARGS;
}
If the original imm exceeds the s16 range (i.e., a jump offset greater
than 32767 instructions), this downcast silently truncates the offset,
resulting in an incorrect call target.
Fix this by:
1. In bpf_patch_call_args(), keeping the imm field unchanged and using the
off field to store the index of the interpreter function.
2. In ___bpf_prog_run() for the JMP_CALL_ARGS case, retrieving the
interpreter function pointer from the interpreters_args array using the
off field as the index, and passing the original imm to calculate the
last argument of the interpreter function.
After these changes, the truncation issue is resolved, and __bpf_call_base_args
is also no longer needed and can be removed, which makes the code cleaner.
Performance: In ___bpf_prog_run() for the JMP_CALL_ARGS case, changing the
retrieval of the interpreter function pointer from pointer addition to
direct array indexing improves performance. The possible reason is that the
latter has better instruction-level parallelism. See the v5 discussion [1]
for more details.
[1] https://lore.kernel.org/bpf/f120c3c4-6999-414a-b514-518bb64b4758@zju.edu.cn/
To avoid requiring bpftool changes, keep the new imm/off encoding internal
and restore the legacy xlated dump layout in bpf_insn_prepare_dump().
For bpf-to-bpf call offsets that do not fit in s16, export off as 0 instead
of a truncated and misleading value.
Fixes: 1ea47e0 ("bpf: add support for bpf_call to interpreter")
Fixes: 7105e82 ("bpf: allow for correlation of maps and helpers in dump")
Suggested-by: Xu Kuohai <xukuohai@huaweicloud.com>
Suggested-by: Puranjay Mohan <puranjay@kernel.org>
Co-developed-by: Tianci Cao <ziye@zju.edu.cn>
Signed-off-by: Tianci Cao <ziye@zju.edu.cn>
Co-developed-by: Shenghao Yuan <shenghaoyuan0928@163.com>
Signed-off-by: Shenghao Yuan <shenghaoyuan0928@163.com>
Signed-off-by: Yazhou Tang <tangyazhou518@outlook.com>
Add a selftest to verify the verifier and JIT behavior when handling
bpf-to-bpf calls with relative jump offsets exceeding the s16 boundary.
The test utilizes an inline assembly block with ".rept 32765" to generate
a massive dummy subprogram. By placing this padding between the main
program and the target subprogram, it forces the verifier to process a
bpf-to-bpf call where the imm field exceeds the s16 range.
- When JIT is enabled, it asserts that the program is successfully loaded
and executes correctly to return the expected value. Since the fix
does not change the JIT behavior, the test passes whether the fix is
applied or not.
- When JIT is disabled, it also asserts that the program is successfully
loaded and executes correctly to return the expected value 3.
- Before the fix, the verifier rewrites the call instruction with a
truncated offset (here 32768 -> -32768) and lets it pass. When the
program is executed, the call instruction will go to a wrong target
(the landing pad) instead of the intended subprogram, then return -1
and fail.
- After the fix, the verifier correctly handles the large offset and
allows it to pass. The program then executes correctly to return the
expected value 3.
Co-developed-by: Tianci Cao <ziye@zju.edu.cn>
Signed-off-by: Tianci Cao <ziye@zju.edu.cn>
Co-developed-by: Shenghao Yuan <shenghaoyuan0928@163.com>
Signed-off-by: Shenghao Yuan <shenghaoyuan0928@163.com>
Signed-off-by: Yazhou Tang <tangyazhou518@outlook.com>
Acked-by: Xu Kuohai <xukuohai@huawei.com>
Author
|
Upstream branch: 2ca6723 |
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Pull request for series with
subject: bpf: Fix call offset truncation and OOB read in bpf_patch_call_args()
version: 10
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1090376