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

Ananth N Mavinakayanahalli
2006-06-01T03:40:22Z

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) {