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

Zachary Amsden
2006-05-31T20:15:44Z

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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) {