x86, fpu: fix 32-bit signal frame handling
From: Dave Hansen <dave.hansen@linux.intel.com>
Background:
Signal frames on x86 have two formats:
1. For 32-bit executables (whether on a real 32-bit kernel or
under ia32 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 werid 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. 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.
This was broken by:
commit 72a671ced66db6d1c2bfff1c930a101ac8d08204
Author: Suresh Siddha <suresh.b.siddha@intel.com>
Date: Tue Jul 24 16:05:29 2012 -0700
x86, fpu: Unify signal handling code paths for x86 and x86_64 kernels
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index ef29b74..31c6a60 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -385,20 +385,19 @@
*/
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;
}
}
