From 6ffac1e90a17ea0aded5c581204397421eec91b6 Mon Sep 17 00:00:00 2001
From: Suresh Siddha <suresh.b.siddha@intel.com>
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 <suresh.b.siddha@intel.com>
Cc: <stable@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
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;
}