From: Peter Zijlstra <peterz@infradead.org>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: x86@kernel.org, jpoimboe@redhat.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: Thu, 14 Oct 2021 12:05:46 +0200 [thread overview]
Message-ID: <YWgA+vbWCdGLZhq5@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <YWb3TdmyPK7GwBP4@hirez.programming.kicks-ass.net>
On Wed, Oct 13, 2021 at 05:12:13PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 13, 2021 at 03:38:27PM +0100, Andrew Cooper wrote:
> > On 13/10/2021 13:22, Peter Zijlstra wrote:
> > > +static int patch_retpoline(void *addr, struct insn *insn, u8 *bytes)
> > > +{
> > > + void (*target)(void);
> > > + int reg, i = 0;
> > > +
> > > + if (cpu_feature_enabled(X86_FEATURE_RETPOLINE))
> > > + return -1;
> > > +
> > > + target = addr + insn->length + insn->immediate.value;
> > > + reg = (target - &__x86_indirect_thunk_rax) /
> > > + (&__x86_indirect_thunk_rcx - &__x86_indirect_thunk_rax);
> >
> > This is equal measures beautiful and terrifying.
>
> Thanks! :-)
Would something like this appease people? If the toolchain can mess this
up everything is broken.
That makes the symtab looks like:
(and arguably, that array symbol could be local)
...
35: 0000000000000000 512 NOTYPE GLOBAL DEFAULT 4 __x86_indirect_thunk_array
36: 0000000000000000 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rax
37: 0000000000000020 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rcx
38: 0000000000000040 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rdx
39: 0000000000000060 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rbx
40: 0000000000000080 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rsp
41: 00000000000000a0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rbp
42: 00000000000000c0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rsi
43: 00000000000000e0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_rdi
44: 0000000000000100 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r8
45: 0000000000000120 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r9
46: 0000000000000140 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r10
47: 0000000000000160 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r11
48: 0000000000000180 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r12
49: 00000000000001a0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r13
50: 00000000000001c0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r14
51: 00000000000001e0 17 FUNC GLOBAL DEFAULT 4 __x86_indirect_thunk_r15
---
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -30,7 +30,7 @@
.align 32
-SYM_FUNC_START(__x86_indirect_thunk_\reg)
+SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL)
ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
__stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \
@@ -55,10 +55,16 @@ SYM_FUNC_END(__x86_indirect_thunk_\reg)
#define __EXPORT_THUNK(sym) _ASM_NOKPROBE(sym); EXPORT_SYMBOL(sym)
#define EXPORT_THUNK(reg) __EXPORT_THUNK(__x86_indirect_thunk_ ## reg)
+ .align 32
+SYM_CODE_START(__x86_indirect_thunk_array)
+
#define GEN(reg) THUNK reg
#include <asm/GEN-for-each-reg.h>
#undef GEN
+ .align 32
+SYM_CODE_END(__x86_indirect_thunk_array)
+
#define GEN(reg) EXPORT_THUNK(reg)
#include <asm/GEN-for-each-reg.h>
#undef GEN
next prev parent reply other threads:[~2021-10-14 10:06 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 [this message]
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
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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