Subject: Re: [PATCH bpf] bpf: fix 32-bit divide by zero

From: Eric Dumazet <[email-masked]>
Date: Thu, 18 Jan 2018 14:30:54 -0800

On Fri, 2018-01-12 at 18:59 -0800, Alexei Starovoitov wrote:
> due to some JITs doing if (src_reg == 0) check in 64-bit mode
> for div/mod opreations mask upper 32-bits of src register
> before doing the check
> 

Is the plan to fix JIT, and if they can all be fixed,
revert this patch ?

x86 patch would be something like :

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 87f214fbe66ec163d24b12b6defc7edab612ecc9..91e4ab69573e09f793eb1c1e29d1b5ffad1d5dc7 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -548,8 +548,13 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
 			if (BPF_SRC(insn->code) == BPF_X) {
 				/* if (src_reg == 0) return 0 */
 
-				/* cmp r11, 0 */
-				EMIT4(0x49, 0x83, 0xFB, 0x00);
+				if (BPF_CLASS(insn->code) == BPF_ALU64) {
+					/* cmp r11, 0 */
+					EMIT4(0x49, 0x83, 0xFB, 0x00);
+				} else {
+					/* cmp r11d, 0 */
+					EMIT4(0x41, 0x83, 0xFB, 0x00);
+				}
 
 				/* jne .+9 (skip over pop, pop, xor and jmp) */
 				EMIT2(X86_JNE, 1 + 1 + 2 + 5);