On Fri, Jan 7, 2022 at 9:11 PM Yichun Zhang (agentzh)
<yichun@xxxxxxxxxxxxx> wrote:
>
> The BPF interpreter always truncates the BPF CALL instruction's 32-bit
> jump offset to 16-bit. Large BPF programs run by the interpreter often
> hit this issue and result in weird behaviors when jumping to the wrong
> destination instructions.
>
> The BPF JIT compiler does not have this bug.
>
> Fixes: 1ea47e01ad6ea ("bpf: add support for bpf_call to interpreter")
> Signed-off-by: Yichun Zhang (agentzh) <yichun@xxxxxxxxxxxxx>
> ---
> kernel/bpf/core.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 2405e39d800f..dc3c90992f33 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -59,6 +59,9 @@
> #define CTX regs[BPF_REG_CTX]
> #define IMM insn->imm
>
> +static u64 (*interpreters_args[])(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5,
> + const struct bpf_insn *insn);
> +
> /* No hurry in this branch
> *
> * Exported for the bpf jit load helper.
> @@ -1560,10 +1563,10 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
> CONT;
>
> JMP_CALL_ARGS:
> - BPF_R0 = (__bpf_call_base_args + insn->imm)(BPF_R1, BPF_R2,
> - BPF_R3, BPF_R4,
> - BPF_R5,
> - insn + insn->off + 1);
> + BPF_R0 = (interpreters_args[insn->off])(BPF_R1, BPF_R2,
> + BPF_R3, BPF_R4,
> + BPF_R5,
> + insn + insn->imm + 1);
> CONT;
>
> JMP_TAIL_CALL: {
> @@ -1810,9 +1813,7 @@ EVAL4(PROG_NAME_LIST, 416, 448, 480, 512)
> 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->off = (round_up(stack_depth, 32) / 32) - 1;
> insn->code = BPF_JMP | BPF_CALL_ARGS;
Neat. Please add a test case and resubmit.
