From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: x86@kernel.org, andrew.cooper3@citrix.com,
linux-kernel@vger.kernel.org, alexei.starovoitov@gmail.com,
ndesaulniers@google.com
Subject: Re: [PATCH 9/9] bpf,x86: Respect X86_FEATURE_RETPOLINE*
Date: Wed, 13 Oct 2021 14:06:05 -0700 [thread overview]
Message-ID: <20211013210605.bz6l7o5xzik5ckga@treble> (raw)
In-Reply-To: <20211013123645.706163435@infradead.org>
On Wed, Oct 13, 2021 at 02:22:26PM +0200, Peter Zijlstra wrote:
> Current BPF codegen doesn't respect X86_FEATURE_RETPOLINE* flags and
> unconditionally emits a thunk call, this is sub-optimal and doesn't
> match the regular, compiler generated, code.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> arch/x86/net/bpf_jit_comp.c | 18 +++++++++++-------
> 1 file changed, 11 insertions(+), 7 deletions(-)
>
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -2123,14 +2123,18 @@ static int emit_fallback_jump(u8 **pprog
> int err = 0;
>
> #ifdef CONFIG_RETPOLINE
> - /* Note that this assumes the the compiler uses external
> - * thunks for indirect calls. Both clang and GCC use the same
> - * naming convention for external thunks.
> - */
> - err = emit_jump(&prog, __x86_indirect_thunk_rdx, prog);
> -#else
> - EMIT2(0xFF, 0xE2); /* jmp rdx */
> + if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) {
> + if (cpu_feature_enabled(X86_FEATURE_RETPOLINE_AMD)) {
> + /* The AMD retpoline can be easily emitted inline. */
> + EMIT3(0x0F, 0xAE, 0xE8); /* lfence */
> + EMIT2(0xFF, 0xE2); /* jmp rdx */
> + } else {
> + /* Call the retpoline thunk */
> + err = emit_jump(&prog, __x86_indirect_thunk_rdx, prog);
> + }
> + } else
> #endif
> + EMIT2(0xFF, 0xE2); /* jmp rdx */
But the rest of eBPF JIT just emits retpolines unconditionally
regardless of feature, for example see RETPOLINE_RCX_BPF_JIT(). So I'm
thinking this should probably be consistent with that (or that with
this).
--
Josh
next prev parent reply other threads:[~2021-10-13 21:06 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-13 12:22 [PATCH 0/9] x86: Rewrite the retpoline rewrite logic Peter Zijlstra
2021-10-13 12:22 ` [PATCH 1/9] objtool,x86: Replace alternatives with .retpoline_sites Peter Zijlstra
2021-10-13 13:29 ` Borislav Petkov
2021-10-13 20:11 ` Josh Poimboeuf
2021-10-14 15:43 ` Peter Zijlstra
2021-10-13 12:22 ` [PATCH 2/9] x86/retpoline: Remove unused replacement symbols Peter Zijlstra
2021-10-13 12:22 ` [PATCH 3/9] x86/asm: Fix register order Peter Zijlstra
2021-10-13 20:15 ` Josh Poimboeuf
2021-10-13 12:22 ` [PATCH 4/9] x86/alternative: Implement .retpoline_sites support Peter Zijlstra
2021-10-13 14:38 ` Andrew Cooper
2021-10-13 15:12 ` Peter Zijlstra
2021-10-13 17:11 ` Andrew Cooper
2021-10-14 10:05 ` Peter Zijlstra
2021-10-13 20:39 ` Josh Poimboeuf
2021-10-13 21:20 ` Peter Zijlstra
2021-10-13 21:49 ` Josh Poimboeuf
2021-10-13 21:52 ` Josh Poimboeuf
2021-10-13 22:10 ` Peter Zijlstra
2021-10-13 22:47 ` Andrew Cooper
2021-10-13 20:52 ` Josh Poimboeuf
2021-10-13 21:00 ` Peter Zijlstra
2021-10-19 11:37 ` Peter Zijlstra
2021-10-19 16:46 ` Josh Poimboeuf
2021-10-19 16:49 ` Josh Poimboeuf
2021-10-20 8:25 ` Peter Zijlstra
2021-10-20 8:30 ` Peter Zijlstra
2021-10-13 21:11 ` Josh Poimboeuf
2021-10-13 21:43 ` Peter Zijlstra
2021-10-13 22:05 ` Josh Poimboeuf
2021-10-13 22:14 ` Peter Zijlstra
2021-10-15 14:24 ` Borislav Petkov
2021-10-15 16:56 ` Peter Zijlstra
2021-10-18 23:06 ` Alexander Lobakin
2021-10-19 0:25 ` Alexander Lobakin
2021-10-19 9:47 ` Alexander Lobakin
2021-10-19 10:16 ` Peter Zijlstra
2021-10-19 15:37 ` Sami Tolvanen
2021-10-19 18:00 ` Alexander Lobakin
2021-10-19 9:40 ` Peter Zijlstra
2021-10-19 10:02 ` Peter Zijlstra
2021-10-13 12:22 ` [PATCH 5/9] x86/alternative: Handle Jcc __x86_indirect_thunk_\reg Peter Zijlstra
2021-10-13 20:11 ` Nick Desaulniers
2021-10-13 21:08 ` Peter Zijlstra
2021-10-13 12:22 ` [PATCH 6/9] x86/alternative: Try inline spectre_v2=retpoline,amd Peter Zijlstra
2021-10-13 12:22 ` [PATCH 7/9] x86/alternative: Add debug prints to apply_retpolines() Peter Zijlstra
2021-10-13 12:22 ` [PATCH 8/9] x86,bugs: Unconditionally allow spectre_v2=retpoline,amd Peter Zijlstra
2021-10-13 12:22 ` [PATCH 9/9] bpf,x86: Respect X86_FEATURE_RETPOLINE* Peter Zijlstra
2021-10-13 21:06 ` Josh Poimboeuf [this message]
2021-10-13 21:54 ` Peter Zijlstra
2021-10-14 9:46 ` Peter Zijlstra
2021-10-14 9:48 ` Peter Zijlstra
2021-10-20 7:34 ` Peter Zijlstra
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