The FXSAVE information leak patch introduced a bug in FP exception
handling: it clears FP exceptions only when there are already
none outstanding.  Mikael Pettersson reported that causes problems
with the Erlang runtime and has tested this fix.
Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Acked-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

AMD K7/K8 CPUs only save/restore the FOP/FIP/FDP x87 registers in FXSAVE
when an exception is pending.  This means the value leak through context
switches and allow processes to observe some x87 instruction state of
other processes.

This was actually documented by AMD, but nobody recognized it as being
different from Intel before.

The fix first adds an optimization: instead of unconditionally calling
FNCLEX after each FXSAVE test if ES is pending and skip it when not
needed. Then do a x87 load from a kernel variable to clear FOP/FIP/FDP.

This means other processes always will only see a constant value defined
by the kernel in their FP state.

I took some pain to make sure to chose a variable that's already in L1
during context switch to make the overhead of this low.

Also alternative() is used to patch away the new code on CPUs who don't
need it.

Patch for both i386/x86-64.

The problem was discovered originally by Jan Beulich. Richard Brunner
provided the basic code for the workarounds, with contribution from Jan.

This is CVE-2006-1056

Cc: richard.brunner@amd.com
Cc: jbeulich@novell.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

This one ends up using an inline asm format that claims to read memory
and then clobber it (rather than just write it directly), which made it
easier to use the existing "alternative_input()" infrastructure support.

Now the fxsave code matches the fxrstor.

It's really just a single instruction, conditional on whether the CPU
supports FXSR or not, so implement it as such instead of making it a
function that queries FXSR dynamically.

This means that the instruction just gets automatically rewritten to the
correct one at boot-time.

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!