x86, fpu: fix 32-bit signal frame handling
From: Dave Hansen <firstname.lastname@example.org>
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"
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.
save_xstate_epilog() uses 'fx_sw_reserved_ia32' whenever it is
called for a 32-bit executable. This is for real 32-bit and
But, fpu__init_prepare_fx_sw_frame() only initializes
'fx_sw_reserved_ia32' when emulation is enabled, *NOT* for real
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:
Author: Suresh Siddha <email@example.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 <firstname.lastname@example.org>
1 file changed