Messages in this thread Patch in this message | | | Date | Thu, 12 Nov 2015 05:28:17 -0800 | From | tip-bot for Dave Hansen <> | Subject | [tip:x86/urgent] x86/fpu: Fix 32-bit signal frame handling |
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Commit-ID: ab6b52947545a5355154f64f449f97af9d05845f Gitweb: http://git.kernel.org/tip/ab6b52947545a5355154f64f449f97af9d05845f Author: Dave Hansen <dave.hansen@linux.intel.com> AuthorDate: Tue, 10 Nov 2015 16:23:54 -0800 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Thu, 12 Nov 2015 09:23:45 +0100
x86/fpu: Fix 32-bit signal frame handling
(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: <stable@vger.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> 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> --- arch/x86/kernel/fpu/signal.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-)
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 @@ fpu__alloc_mathframe(unsigned long sp, int ia32_frame, */ 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; } }
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