Re: [PATCH bpf] bpf: use NOP_ATOMIC5 instead of emit_nops(&prog, 5) for BPF_TRAMP_F_CALL_ORIG
From: Yauheni Kaliuta <hidden>
Date: 2021-03-22 06:40:37
Also in:
bpf
On Sat, Mar 20, 2021 at 2:01 AM Stanislav Fomichev [off-list ref] wrote:
__bpf_arch_text_poke does rewrite only for atomic nop5, emit_nops(xxx, 5)
emits non-atomic one which breaks fentry/fexit with k8 atomics:
P6_NOP5 == P6_NOP5_ATOMIC (0f1f440000 == 0f1f440000)
K8_NOP5 != K8_NOP5_ATOMIC (6666906690 != 6666666690)
Can be reproduced by doing "ideal_nops = k8_nops" in "arch_init_ideal_nops()
and running fexit_bpf2bpf selftest.
Fixes: e21aa341785c ("bpf: Fix fexit trampoline.")
Signed-off-by: Stanislav Fomichev <redacted>Could you mention x86 in the subject?
quoted hunk ↗ jump to hunk
--- 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 72b5a57e9e31..b35fc8023884 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c@@ -2012,7 +2012,8 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i /* remember return value in a stack for bpf prog to access */ emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8); im->ip_after_call = prog; - emit_nops(&prog, 5); + memcpy(prog, ideal_nops[NOP_ATOMIC5], X86_PATCH_SIZE); + prog += X86_PATCH_SIZE; } if (fmod_ret->nr_progs) { --2.31.0.rc2.261.g7f71774620-goog
-- WBR, Yauheni