[PATCH] ix86: really make user_mode() work correctly for VM86 mode

[PATCH] ix86: really make user_mode() work correctly for VM86 mode

[Jan Beulich]

While commit efa7045103 ("x86/asm/entry: Make user_mode() work
correctly if regs came from VM86 mode") claims that "user_mode() is now
identical to user_mode_vm()", this wasn't actually the case - no prior
commit made it so.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/include/asm/ptrace.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- 4.1-rc5/arch/x86/include/asm/ptrace.h
+++ 4.1-rc5-ix86-user_mode/arch/x86/include/asm/ptrace.h
@@ -107,7 +107,8 @@ static inline unsigned long regs_return_
 static inline int user_mode(struct pt_regs *regs)
 {
 #ifdef CONFIG_X86_32
-	return (regs->cs & SEGMENT_RPL_MASK) == USER_RPL;
+	return ((regs->cs & SEGMENT_RPL_MASK) | (regs->flags & X86_VM_MASK))
+	       >= USER_RPL;
 #else
 	return !!(regs->cs & 3);
 #endif

Re: [PATCH] ix86: really make user_mode() work correctly for VM86 mode

[Andy Lutomirski]

On May 28, 2015 1:16 AM, "Jan Beulich" <JBeulich@suse.com> wrote:
>
> While commit efa7045103 ("x86/asm/entry: Make user_mode() work
> correctly if regs came from VM86 mode") claims that "user_mode() is now
> identical to user_mode_vm()", this wasn't actually the case - no prior
> commit made it so.

That's embarrassing!  I'm not sure how I screwed that up.

Acked-by: Andy Lutomirski <luto@kernel.org>

This is needed for x86/urgent.  I'll see if I can write a simple test
case, too.  My old do_bounds test should be a good start.

--Andy

Re: [PATCH] ix86: really make user_mode() work correctly for VM86 mode

[Ingo Molnar]

* Andy Lutomirski <luto@amacapital.net> wrote:

> On May 28, 2015 1:16 AM, "Jan Beulich" <JBeulich@suse.com> wrote:
> >
> > While commit efa7045103 ("x86/asm/entry: Make user_mode() work
> > correctly if regs came from VM86 mode") claims that "user_mode() is now
> > identical to user_mode_vm()", this wasn't actually the case - no prior
> > commit made it so.
> 
> That's embarrassing!  I'm not sure how I screwed that up.

I should have noticed it too :-/

In fact I remember that I wanted to double check it all because the algorithmic 
complexity of the new test looked suspiciously too simple on the 32-bit side (we 
_did_ have a legitimate reason to keep the API split originally) - but forgot 
about it.

> Acked-by: Andy Lutomirski <luto@kernel.org>
> 
> This is needed for x86/urgent.

Yeah, queued it up.

> [...]  I'll see if I can write a simple test case, too.  My old do_bounds test 
> should be a good start.

That kind of test would be absolutely fantastic to have.

Thanks,

	Ingo

[tip:x86/urgent] x86/asm/entry/32: Really make user_mode() work correctly for VM86 mode

[tip-bot for Jan Beulich]

Commit-ID:  7ba554b5ac69e5f3edac9ce3233beb5acd480878
Gitweb:     http://git.kernel.org/tip/7ba554b5ac69e5f3edac9ce3233beb5acd480878
Author:     Jan Beulich <JBeulich@suse.com>
AuthorDate: Thu, 28 May 2015 09:16:45 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 29 May 2015 09:46:40 +0200

x86/asm/entry/32: Really make user_mode() work correctly for VM86 mode

While commit efa7045103 ("x86/asm/entry: Make user_mode() work
correctly if regs came from VM86 mode") claims that "user_mode()
is now identical to user_mode_vm()", this wasn't actually the
case - no prior commit made it so.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/5566EB0D020000780007E655@mail.emea.novell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/ptrace.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 19507ff..5fabf13 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -107,7 +107,7 @@ static inline unsigned long regs_return_value(struct pt_regs *regs)
 static inline int user_mode(struct pt_regs *regs)
 {
 #ifdef CONFIG_X86_32
-	return (regs->cs & SEGMENT_RPL_MASK) == USER_RPL;
+	return ((regs->cs & SEGMENT_RPL_MASK) | (regs->flags & X86_VM_MASK)) >= USER_RPL;
 #else
 	return !!(regs->cs & 3);
 #endif