From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: x86@kernel.org, andrew.cooper3@citrix.com,
linux-kernel@vger.kernel.org, alexei.starovoitov@gmail.com,
ndesaulniers@google.com
Subject: Re: [PATCH 4/9] x86/alternative: Implement .retpoline_sites support
Date: Wed, 13 Oct 2021 23:00:15 +0200 [thread overview]
Message-ID: <YWdI31noOUQVSA6w@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20211013205259.44cvvaxiexiff5w5@treble>
On Wed, Oct 13, 2021 at 01:52:59PM -0700, Josh Poimboeuf wrote:
> On Wed, Oct 13, 2021 at 02:22:21PM +0200, Peter Zijlstra wrote:
> > /*
> > + * Rewrite the retpolines, must be done before alternatives since
> > + * those can rewrite the retpoline thunks.
> > + */
>
> Why exactly is that a problem? This code doesn't read the thunks.
The below problem :-) I didn't include it in the series, but I'm
thinking that's where I wants to go eventually.
---
Subject: x86,retpoline: Poison retpoline thunks for !X86_FEATURE_RETPOLINE
From: Peter Zijlstra <peterz@infradead.org>
Date: Tue Oct 12 10:30:56 CEST 2021
Now that objtool will out-of-line all retpoline thunk calls for
!RETPOLINE, poison them.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/lib/retpoline.S | 10 ++++++++++
1 file changed, 10 insertions(+)
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -32,9 +32,19 @@
SYM_FUNC_START(__x86_indirect_thunk_\reg)
+#ifdef CONFIG_STACK_VALIDATION
+/*
+ * When objtool runs, there should not be any __x86_indirect_thunk_* calls
+ * left after alternatives, ensure this by patching it to UD2.
+ */
+ ALTERNATIVE_2 __stringify(RETPOLINE \reg), \
+ __stringify(ud2), ALT_NOT(X86_FEATURE_RETPOLINE), \
+ __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD
+#else
ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
__stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \
__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD
+#endif
SYM_FUNC_END(__x86_indirect_thunk_\reg)
next prev parent reply other threads:[~2021-10-13 21:03 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 [this message]
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
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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