linux-kernel - [tip:x86/urgent] x86, paravirt: prevent gcc from generating the wrong addressing mode

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Date:	Tue, 17 Mar 2009 02:12:34 GMT
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, jeremy@...p.org, hpa@...or.com,
	mingo@...hat.com, akataria@...are.com, tglx@...utronix.de,
	jeremy.fitzhardinge@...rix.com
Subject: [tip:x86/urgent] x86, paravirt: prevent gcc from generating the wrong addressing mode

Commit-ID:  42854dc0a6320ff36722749acafa0697522d9556
Gitweb:     http://git.kernel.org/tip/42854dc0a6320ff36722749acafa0697522d9556
Author:     Jeremy Fitzhardinge <jeremy@...p.org>
AuthorDate: Mon, 16 Mar 2009 17:24:34 -0700
Commit:     H. Peter Anvin <hpa@...or.com>
CommitDate: Mon, 16 Mar 2009 18:36:31 -0700

x86, paravirt: prevent gcc from generating the wrong addressing mode

Impact: fix crash on VMI (VMware)

When we generate a call sequence for calling a paravirtualized
function, we presume that the generated code is "call *0xXXXXX",
which is a 6 byte opcode; this is larger than a normal
direct call, and so we can patch a direct call over it.

At the moment, however we give gcc enough rope to hang us by
putting the address in a register and generating a two byte
indirect-via-register call.  Prevent this by explicitly
dereferencing the function pointer and passing it into the
asm as a constant.

This prevents crashes in VMI, as it cannot handle unpatchable
callsites.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Cc: Alok Kataria <akataria@...are.com>
LKML-Reference: <49BEEDC2.2070809@...p.org>
Signed-off-by: H. Peter Anvin <hpa@...or.com>


---
 arch/x86/include/asm/paravirt.h |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index e299287..0c212d5 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -360,7 +360,7 @@ extern struct pv_lock_ops pv_lock_ops;
 
 #define paravirt_type(op)				\
 	[paravirt_typenum] "i" (PARAVIRT_PATCH(op)),	\
-	[paravirt_opptr] "m" (op)
+	[paravirt_opptr] "i" (&(op))
 #define paravirt_clobber(clobber)		\
 	[paravirt_clobber] "i" (clobber)
 
@@ -412,7 +412,7 @@ int paravirt_disable_iospace(void);
  * offset into the paravirt_patch_template structure, and can therefore be
  * freely converted back into a structure offset.
  */
-#define PARAVIRT_CALL	"call *%[paravirt_opptr];"
+#define PARAVIRT_CALL	"call *%c[paravirt_opptr];"
 
 /*
  * These macros are intended to wrap calls through one of the paravirt
--
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