lkml.org 
[lkml]   [2015]   [Dec]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 4.3 049/125] x86/fpu: Fix 32-bit signal frame handling
Date
4.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dave Hansen <dave.hansen@linux.intel.com>

commit ab6b52947545a5355154f64f449f97af9d05845f upstream.

(This should have gone to LKML originally. Sorry for the extra
noise, folks on the cc.)

Background:

Signal frames on x86 have two formats:

1. For 32-bit executables (whether on a real 32-bit kernel or
under 32-bit emulation on a 64-bit kernel) we have a
'fpregset_t' that includes the "FSAVE" registers.

2. For 64-bit executables (on 64-bit kernels obviously), the
'fpregset_t' is smaller and does not contain the "FSAVE"
state.

When creating the signal frame, we have to be aware of whether
we are running a 32 or 64-bit executable so we create the
correct format signal frame.

Problem:

save_xstate_epilog() uses 'fx_sw_reserved_ia32' whenever it is
called for a 32-bit executable. This is for real 32-bit and
ia32 emulation.

But, fpu__init_prepare_fx_sw_frame() only initializes
'fx_sw_reserved_ia32' when emulation is enabled, *NOT* for real
32-bit kernels.

This leads to really wierd situations where 32-bit programs
lose their extended state when returning from a signal handler.
The kernel copies the uninitialized (zero) 'fx_sw_reserved_ia32'
out to userspace in save_xstate_epilog(). But when returning
from the signal, the kernel errors out in check_for_xstate()
when it does not see FP_XSTATE_MAGIC1 present (because it was
zeroed). This leads to the FPU/XSAVE state being initialized.

For MPX, this leads to the most permissive state and means we
silently lose bounds violations. I think this would also mean
that we could lose *ANY* FPU/SSE/AVX state. I'm not sure why
no one has spotted this bug.

I believe this was broken by:

72a671ced66d ("x86, fpu: Unify signal handling code paths for x86 and x86_64 kernels")

way back in 2012.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
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>
Cc: dave@sr71.net
Cc: fenghua.yu@intel.com
Cc: yu-cheng.yu@intel.com
Link: http://lkml.kernel.org/r/20151111002354.A0799571@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kernel/fpu/signal.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)

--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -385,20 +385,19 @@ fpu__alloc_mathframe(unsigned long sp, i
*/
void fpu__init_prepare_fx_sw_frame(void)
{
- int fsave_header_size = sizeof(struct fregs_state);
int size = xstate_size + FP_XSTATE_MAGIC2_SIZE;

- if (config_enabled(CONFIG_X86_32))
- size += fsave_header_size;
-
fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
fx_sw_reserved.extended_size = size;
fx_sw_reserved.xfeatures = xfeatures_mask;
fx_sw_reserved.xstate_size = xstate_size;

- if (config_enabled(CONFIG_IA32_EMULATION)) {
+ if (config_enabled(CONFIG_IA32_EMULATION) ||
+ config_enabled(CONFIG_X86_32)) {
+ int fsave_header_size = sizeof(struct fregs_state);
+
fx_sw_reserved_ia32 = fx_sw_reserved;
- fx_sw_reserved_ia32.extended_size += fsave_header_size;
+ fx_sw_reserved_ia32.extended_size = size + fsave_header_size;
}
}




\
 
 \ /
  Last update: 2015-12-07 16:41    [W:0.425 / U:0.924 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site