linux-kernel - [PATCH v2] x86: Fix code patching for paravirt-alternatives on 486

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <1252547631.3423.134.camel@localhost>
Date:	Thu, 10 Sep 2009 02:53:50 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	x86@...nel.org
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: [PATCH v2] x86: Fix code patching for paravirt-alternatives on 486

As reported in <http://bugs.debian.org/511703> and
<http://bugs.debian.org/515982>, kernels with paravirt-alternatives
enabled crash in text_poke_early() on at least some 486-class
processors.

The problem is that text_poke_early() itself uses inline functions
affected by paravirt-alternatives and so will modify instructions that
have already been prefetched.  Pentium and later processors will
invalidate the prefetched instructions in this case, but 486-class
processors do not.

Change sync_core() to limit prefetching on 486-class (and 386-class)
processors, and move the call to sync_core() above the call to the
modifiable local_irq_restore().

Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
Second try, incorporating the jmp into sync_core().

Also not signed as I know git has trouble with MIME.

Ben.

 arch/x86/include/asm/processor.h |   16 +++++++++++++---
 arch/x86/kernel/alternative.c    |    2 +-
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index c776826..2db56c5 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -703,13 +703,23 @@ static inline void cpu_relax(void)
 	rep_nop();
 }
 
-/* Stop speculative execution: */
+/* Stop speculative execution and prefetching of modified code. */
 static inline void sync_core(void)
 {
 	int tmp;
 
-	asm volatile("cpuid" : "=a" (tmp) : "0" (1)
-		     : "ebx", "ecx", "edx", "memory");
+#if defined(CONFIG_M386) || defined(CONFIG_M486)
+	if (boot_cpu_data.x86 < 5)
+		/* There is no speculative execution.
+		 * jmp is a barrier to prefetching. */
+		asm volatile("jmp 1f\n1:\n" ::: "memory");
+	else
+#endif
+		/* cpuid is a barrier to speculative execution.
+		 * Prefetched instructions are automatically
+		 * invalidated when modified. */
+		asm volatile("cpuid" : "=a" (tmp) : "0" (1)
+			     : "ebx", "ecx", "edx", "memory");
 }
 
 static inline void __monitor(const void *eax, unsigned long ecx,
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 4869351..de7353c 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -498,8 +498,8 @@ static void *__init_or_module text_poke_early(void *addr, const void *opcode,
 	unsigned long flags;
 	local_irq_save(flags);
 	memcpy(addr, opcode, len);
-	local_irq_restore(flags);
 	sync_core();
+	local_irq_restore(flags);
 	/* Could also do a CLFLUSH here to speed up CPU recovery; but
 	   that causes hangs on some VIA CPUs. */
 	return addr;
-- 
1.6.3.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/