Re: + i386-fix-get_segment_eip-with-vm86.patch added to -mm tree

Re: + i386-fix-get_segment_eip-with-vm86.patch added to -mm tree

[Zachary Amsden]

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akpm@osdl.org wrote:
> The patch titled
>
>      i386: fix get_segment_eip() with vm86 segments
>
> has been added to the -mm tree.  Its filename is
>
>      i386-fix-get_segment_eip-with-vm86.patch
>
> See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
> out what to do about this
>
> ------------------------------------------------------
> Subject: i386: fix get_segment_eip() with vm86 segments
> From: Chuck Ebbert <76306.1226@compuserve.com>
>
>
> We need to check for vm86 mode first before looking at selector privilege
> bits.
>
> Segment limit is always base + 64k and only the low 16 bits of EIP are
> significant in vm86 mode.
>
> Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
> Cc: Andi Kleen <ak@muc.de>
> Cc: Zachary Amsden <zach@vmware.com>
> Cc: Rohit Seth <rohitseth@google.com>
> Signed-off-by: Andrew Morton <akpm@osdl.org>
> ---
>
>  arch/i386/mm/fault.c |   11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff -puN arch/i386/mm/fault.c~i386-fix-get_segment_eip-with-vm86 arch/i386/mm/fault.c
> --- devel/arch/i386/mm/fault.c~i386-fix-get_segment_eip-with-vm86	2006-05-29 20:06:19.000000000 -0700
> +++ devel-akpm/arch/i386/mm/fault.c	2006-05-29 20:06:19.000000000 -0700
> @@ -77,12 +77,15 @@ static inline unsigned long get_segment_
>  	unsigned seg = regs->xcs & 0xffff;
>  	u32 seg_ar, seg_limit, base, *desc;
>  
> +	/* Unlikely, but must come before segment checks. */
> +	if (unlikely(regs->eflags & VM_MASK)) {
> +		base = seg << 4;
> +		*eip_limit = base + 0xffff;
> +		return base + (eip & 0xffff);
> +	}
> +
>  	/* The standard kernel/user address space limit. */
>  	*eip_limit = (seg & 3) ? USER_DS.seg : KERNEL_DS.seg;
> -
> -	/* Unlikely, but must come before segment checks. */
> -	if (unlikely((regs->eflags & VM_MASK) != 0))
> -		return eip + (seg << 4);
>  	
>  	/* By far the most common cases. */
>  	if (likely(seg == __USER_CS || seg == __KERNEL_CS))
> _
>
> Patches currently in -mm which might be from 76306.1226@compuserve.com are
>
> i386-let-usermode-execute-the-enter.patch
> i386-fix-get_segment_eip-with-vm86.patch
>
>   

This looks great.  While we're in the spirit let's fix kprobes v8086 
handling as well by filtering out int3s from v8086 mode.

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Never allow int3 traps from V8086 mode to enter the kprobes handler.

Signed-off-by: Zachary Amsden <zach@vmware.com>

Index: linux-2.6.17-rc/arch/i386/kernel/kprobes.c
===================================================================
--- linux-2.6.17-rc.orig/arch/i386/kernel/kprobes.c	2006-05-18 13:31:50.000000000 -0700
+++ linux-2.6.17-rc/arch/i386/kernel/kprobes.c	2006-05-31 13:09:26.000000000 -0700
@@ -607,7 +607,7 @@ int __kprobes kprobe_exceptions_notify(s
 	struct die_args *args = (struct die_args *)data;
 	int ret = NOTIFY_DONE;
 
-	if (args->regs && user_mode(args->regs))
+	if (args->regs && user_mode_vm(args->regs))
 		return ret;
 
 	switch (val) {

Re: + i386-fix-get_segment_eip-with-vm86.patch added to -mm tree

[Ananth N Mavinakayanahalli]

On Wed, May 31, 2006 at 01:15:42PM -0700, Zachary Amsden wrote:
> akpm@osdl.org wrote:
> >The patch titled
> >
> >     i386: fix get_segment_eip() with vm86 segments
> >
> >has been added to the -mm tree.  Its filename is
> >
> >     i386-fix-get_segment_eip-with-vm86.patch
> >
> >See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
> >out what to do about this
> >
> >------------------------------------------------------
> >Subject: i386: fix get_segment_eip() with vm86 segments
> >From: Chuck Ebbert <76306.1226@compuserve.com>
> >
> >
> >We need to check for vm86 mode first before looking at selector privilege
> >bits.
> >
> >Segment limit is always base + 64k and only the low 16 bits of EIP are
> >significant in vm86 mode.
> >
> >Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
> >Cc: Andi Kleen <ak@muc.de>
> >Cc: Zachary Amsden <zach@vmware.com>
> >Cc: Rohit Seth <rohitseth@google.com>
> >Signed-off-by: Andrew Morton <akpm@osdl.org>
> >---
> >
> > arch/i386/mm/fault.c |   11 +++++++----
> > 1 file changed, 7 insertions(+), 4 deletions(-)
> >
> >diff -puN arch/i386/mm/fault.c~i386-fix-get_segment_eip-with-vm86 
> >arch/i386/mm/fault.c
> >--- devel/arch/i386/mm/fault.c~i386-fix-get_segment_eip-with-vm86 
> >2006-05-29 20:06:19.000000000 -0700
> >+++ devel-akpm/arch/i386/mm/fault.c	2006-05-29 20:06:19.000000000 -0700
> >@@ -77,12 +77,15 @@ static inline unsigned long get_segment_
> > 	unsigned seg = regs->xcs & 0xffff;
> > 	u32 seg_ar, seg_limit, base, *desc;
> > 
> >+	/* Unlikely, but must come before segment checks. */
> >+	if (unlikely(regs->eflags & VM_MASK)) {
> >+		base = seg << 4;
> >+		*eip_limit = base + 0xffff;
> >+		return base + (eip & 0xffff);
> >+	}
> >+
> > 	/* The standard kernel/user address space limit. */
> > 	*eip_limit = (seg & 3) ? USER_DS.seg : KERNEL_DS.seg;
> >-
> >-	/* Unlikely, but must come before segment checks. */
> >-	if (unlikely((regs->eflags & VM_MASK) != 0))
> >-		return eip + (seg << 4);
> > 	
> > 	/* By far the most common cases. */
> > 	if (likely(seg == __USER_CS || seg == __KERNEL_CS))
> >_
> >
> >Patches currently in -mm which might be from 76306.1226@compuserve.com are
> >
> >i386-let-usermode-execute-the-enter.patch
> >i386-fix-get_segment_eip-with-vm86.patch
> >
> >  
> 
> This looks great.  While we're in the spirit let's fix kprobes v8086 
> handling as well by filtering out int3s from v8086 mode.

> Never allow int3 traps from V8086 mode to enter the kprobes handler.
> 
> Signed-off-by: Zachary Amsden <zach@vmware.com>

Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

> 
> Index: linux-2.6.17-rc/arch/i386/kernel/kprobes.c
> ===================================================================
> --- linux-2.6.17-rc.orig/arch/i386/kernel/kprobes.c	2006-05-18 13:31:50.000000000 -0700
> +++ linux-2.6.17-rc/arch/i386/kernel/kprobes.c	2006-05-31 13:09:26.000000000 -0700
> @@ -607,7 +607,7 @@ int __kprobes kprobe_exceptions_notify(s
>  	struct die_args *args = (struct die_args *)data;
>  	int ret = NOTIFY_DONE;
>  
> -	if (args->regs && user_mode(args->regs))
> +	if (args->regs && user_mode_vm(args->regs))
>  		return ret;
>  
>  	switch (val) {