From: Peter Zijlstra <peterz@infradead.org>
To: jpoimboe@redhat.com, alexandre.chartre@oracle.com
Cc: linux-kernel@vger.kernel.org, jthierry@redhat.com,
tglx@linutronix.de, x86@kernel.org, mbenes@suse.cz,
peterz@infradead.org
Subject: [PATCH v2 03/14] x86,smap: Fix smap_{save,restore}() alternatives
Date: Tue, 28 Apr 2020 21:11:04 +0200 [thread overview]
Message-ID: <20200428191659.558899462@infradead.org> (raw)
In-Reply-To: 20200428191101.886208539@infradead.org
As reported by objtool:
lib/ubsan.o: warning: objtool: .altinstr_replacement+0x0: alternative modifies stack
lib/ubsan.o: warning: objtool: .altinstr_replacement+0x7: alternative modifies stack
the smap_{save,restore}() alternatives violate (the newly enforced)
rule on stack invariance. That is, due to there only being a single
ORC table it must be valid to any alternative. These alternatives
violate this with the direct result that unwinds will not be correct
in between these calls.
[ In specific, since we force SMAP on for objtool, running on !SMAP
hardware will observe a different stack-layout and the ORC unwinder
will stumble. ]
So rewrite the functions to unconditionally save/restore the flags,
which gives an invariant stack layout irrespective of the SMAP state.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/smap.h | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
--- a/arch/x86/include/asm/smap.h
+++ b/arch/x86/include/asm/smap.h
@@ -57,16 +57,19 @@ static __always_inline unsigned long sma
{
unsigned long flags;
- asm volatile (ALTERNATIVE("", "pushf; pop %0; " __ASM_CLAC,
- X86_FEATURE_SMAP)
- : "=rm" (flags) : : "memory", "cc");
+ asm volatile ("# smap_save\n\t"
+ "pushf; pop %0"
+ : "=rm" (flags) : : "memory");
+
+ clac();
return flags;
}
static __always_inline void smap_restore(unsigned long flags)
{
- asm volatile (ALTERNATIVE("", "push %0; popf", X86_FEATURE_SMAP)
+ asm volatile ("# smap_restore\n\t"
+ "push %0; popf"
: : "g" (flags) : "memory", "cc");
}
next prev parent reply other threads:[~2020-04-28 19:19 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-28 19:11 [PATCH v2 00/14] objtool vs retpoline Peter Zijlstra
2020-04-28 19:11 ` [PATCH v2 01/14] objtool: Allow branches within the same alternative Peter Zijlstra
2020-04-28 19:53 ` Josh Poimboeuf
2020-04-28 19:11 ` [PATCH v2 02/14] objtool: Fix ORC vs alternatives Peter Zijlstra
2020-04-28 19:55 ` Josh Poimboeuf
2020-04-29 14:33 ` Miroslav Benes
2020-04-29 15:51 ` Peter Zijlstra
2020-04-29 16:41 ` Miroslav Benes
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2020-04-28 19:11 ` Peter Zijlstra [this message]
2020-04-29 0:54 ` [PATCH v2 03/14] x86,smap: Fix smap_{save,restore}() alternatives Brian Gerst
2020-04-29 8:30 ` Peter Zijlstra
2020-04-29 10:18 ` Peter Zijlstra
2020-04-29 12:12 ` Brian Gerst
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2020-04-28 19:11 ` [PATCH v2 04/14] objtool: is_fentry_call() crashes if call has no destination Peter Zijlstra
2020-04-28 19:11 ` [PATCH v2 05/14] objtool: UNWIND_HINT_RET_OFFSET should not check registers Peter Zijlstra
2020-04-28 19:11 ` [PATCH v2 06/14] objtool: Rework allocating stack_ops on decode Peter Zijlstra
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2020-04-28 19:11 ` [PATCH v2 07/14] objtool: Make handle_insn_ops() unconditional Peter Zijlstra
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2020-05-07 12:38 ` Peter Zijlstra
2020-04-28 19:11 ` [PATCH v2 08/14] objtool: Remove INSN_STACK Peter Zijlstra
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2020-04-28 19:11 ` [PATCH v2 09/14] objtool: Move the IRET hack into the arch decoder Peter Zijlstra
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Miroslav Benes
2020-04-28 19:11 ` [PATCH v2 10/14] objtool: Add support for intra-function calls Peter Zijlstra
2020-04-28 19:11 ` [PATCH v2 11/14] x86/speculation: Change FILL_RETURN_BUFFER to work with objtool Peter Zijlstra
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2020-04-28 19:11 ` [PATCH v2 12/14] x86: Simplify retpoline declaration Peter Zijlstra
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2020-04-28 19:11 ` [PATCH v2 13/14] x86: Change {JMP,CALL}_NOSPEC argument Peter Zijlstra
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2020-04-28 19:11 ` [PATCH v2 14/14] x86/retpoline: Fix retpoline unwind Peter Zijlstra
2020-05-01 18:22 ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2020-04-28 20:17 ` [PATCH v2 00/14] objtool vs retpoline Josh Poimboeuf
2020-04-29 10:19 ` [PATCH v2.1 01-A/14] objtool: Remove check preventing branches within alternative Peter Zijlstra
2020-04-29 10:21 ` [PATCH v2.1 01-B/14] objtool: Uniquely identify alternative instruction groups Peter Zijlstra
2020-04-29 16:46 ` [PATCH v2 00/14] objtool vs retpoline Miroslav Benes
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