[PATCH] x86-paravirt: prevent gcc from generating the wrong addressing mode

[PATCH] x86-paravirt: prevent gcc from generating the wrong addressing mode

[Jeremy Fitzhardinge]

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@citrix.com>
Cc: Alok Kataria <akataria@vmware.com>

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index d4fec1f..6922d16 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -395,7 +395,7 @@ 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)
 
@@ -449,7 +449,7 @@ 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

Re: [PATCH] x86-paravirt: prevent gcc from generating the wrong addressing mode

[Alok Kataria]

Thanks Jeremy.

Acked-by: Alok N Kataria <akataria@vmware.com>

On Mon, 2009-03-16 at 17:24 -0700, Jeremy Fitzhardinge wrote:
> 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@citrix.com>
> Cc: Alok Kataria <akataria@vmware.com>
> 
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index d4fec1f..6922d16 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -395,7 +395,7 @@ 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)
>  
> @@ -449,7 +449,7 @@ 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
> 
> 

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

[Jeremy Fitzhardinge]

Commit-ID:  42854dc0a6320ff36722749acafa0697522d9556
Gitweb:     http://git.kernel.org/tip/42854dc0a6320ff36722749acafa0697522d9556
Author:     Jeremy Fitzhardinge <jeremy@goop.org>
AuthorDate: Mon, 16 Mar 2009 17:24:34 -0700
Commit:     H. Peter Anvin <hpa@zytor.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@citrix.com>
Cc: Alok Kataria <akataria@vmware.com>
LKML-Reference: <49BEEDC2.2070809@goop.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.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