From 6ffac1e90a17ea0aded5c581204397421eec91b6 Mon Sep 17 00:00:00 2001 From: Suresh Siddha Date: Thu, 24 Jul 2008 18:07:56 -0700 Subject: [PATCH] x64, fpu: fix possible FPU leakage in error conditions On Thu, Jul 24, 2008 at 03:43:44PM -0700, Linus Torvalds wrote: > So how about this patch as a starting point? This is the RightThing(tm) to > do regardless, and if it then makes it easier to do some other cleanups, > we should do it first. What do you think? restore_fpu_checking() calls init_fpu() in error conditions. While this is wrong(as our main intention is to clear the fpu state of the thread), this was benign before commit 92d140e21f1 ("x86: fix taking DNA during 64bit sigreturn"). Post commit 92d140e21f1, live FPU registers may not belong to this process at this error scenario. In the error condition for restore_fpu_checking() (especially during the 64bit signal return), we are doing init_fpu(), which saves the live FPU register state (possibly belonging to some other process context) into the thread struct (through unlazy_fpu() in init_fpu()). This is wrong and can leak the FPU data. For the signal handler restore error condition in restore_i387(), clear the fpu state present in the thread struct(before ultimately sending a SIGSEGV for badframe). For the paranoid error condition check in math_state_restore(), send a SIGSEGV, if we fail to restore the state. Signed-off-by: Suresh Siddha Cc: Cc: Linus Torvalds Signed-off-by: Ingo Molnar --- arch/x86/kernel/signal_64.c | 11 ++++++++++- arch/x86/kernel/traps_64.c | 9 ++++++++- include/asm-x86/i387.h | 2 -- 3 files changed, 18 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/signal_64.c b/arch/x86/kernel/signal_64.c index b45ef8ddd651..ca316b5b742c 100644 --- a/arch/x86/kernel/signal_64.c +++ b/arch/x86/kernel/signal_64.c @@ -104,7 +104,16 @@ static inline int restore_i387(struct _fpstate __user *buf) clts(); task_thread_info(current)->status |= TS_USEDFPU; } - return restore_fpu_checking((__force struct i387_fxsave_struct *)buf); + err = restore_fpu_checking((__force struct i387_fxsave_struct *)buf); + if (unlikely(err)) { + /* + * Encountered an error while doing the restore from the + * user buffer, clear the fpu state. + */ + clear_fpu(tsk); + clear_used_math(); + } + return err; } /* diff --git a/arch/x86/kernel/traps_64.c b/arch/x86/kernel/traps_64.c index 3f18d73f420c..513caaca7115 100644 --- a/arch/x86/kernel/traps_64.c +++ b/arch/x86/kernel/traps_64.c @@ -1131,7 +1131,14 @@ asmlinkage void math_state_restore(void) } clts(); /* Allow maths ops (or we recurse) */ - restore_fpu_checking(&me->thread.xstate->fxsave); + /* + * Paranoid restore. send a SIGSEGV if we fail to restore the state. + */ + if (unlikely(restore_fpu_checking(&me->thread.xstate->fxsave))) { + stts(); + force_sig(SIGSEGV, me); + return; + } task_thread_info(me)->status |= TS_USEDFPU; me->fpu_counter++; } diff --git a/include/asm-x86/i387.h b/include/asm-x86/i387.h index 96fa8449ff11..0048fb77afc4 100644 --- a/include/asm-x86/i387.h +++ b/include/asm-x86/i387.h @@ -62,8 +62,6 @@ static inline int restore_fpu_checking(struct i387_fxsave_struct *fx) #else : [fx] "cdaSDb" (fx), "m" (*fx), "0" (0)); #endif - if (unlikely(err)) - init_fpu(current); return err; }