On 6/15/22 5:17 PM, Jakub Sitnicki wrote:
[...]
int entry(struct __sk_buff * skb):
0xffffffffa0201788: nop DWORD PTR [rax+rax*1+0x0]
0xffffffffa020178d: xor eax,eax
0xffffffffa020178f: push rbp
0xffffffffa0201790: mov rbp,rsp
0xffffffffa0201793: sub rsp,0x8
0xffffffffa020179a: push rax
0xffffffffa020179b: xor esi,esi
0xffffffffa020179d: mov BYTE PTR [rbp-0x1],sil
0xffffffffa02017a1: mov rax,QWORD PTR [rbp-0x9] !!! tail call count
0xffffffffa02017a8: call 0xffffffffa02017d8 !!! is at rbp-0x10
0xffffffffa02017ad: leave
0xffffffffa02017ae: ret
Fix it by rounding up the BPF stack depth to a multiple of 8, when
calculating the tail call count offset on stack.
Fixes: ebf7d1f508a7 ("bpf, x64: rework pro/epilogue and tailcall handling in JIT")
Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
---
arch/x86/net/bpf_jit_comp.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index f298b18a9a3d..c98b8c0ed3b8 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1420,8 +1420,9 @@ st: if (is_imm8(insn->off))
case BPF_JMP | BPF_CALL:
func = (u8 *) __bpf_call_base + imm32;
if (tail_call_reachable) {
+ /* mov rax, qword ptr [rbp - rounded_stack_depth - 8] */
EMIT3_off32(0x48, 0x8B, 0x85,
- -(bpf_prog->aux->stack_depth + 8));
+ -round_up(bpf_prog->aux->stack_depth, 8) - 8);
Lgtm, great catch by the way!
