linux/arch/sparc
David S. Miller 44922150d8 sparc64: Fix userspace FPU register corruptions.
If we have a series of events from userpsace, with %fprs=FPRS_FEF,
like follows:

ETRAP
	ETRAP
		VIS_ENTRY(fprs=0x4)
		VIS_EXIT
		RTRAP (kernel FPU restore with fpu_saved=0x4)
	RTRAP

We will not restore the user registers that were clobbered by the FPU
using kernel code in the inner-most trap.

Traps allocate FPU save slots in the thread struct, and FPU using
sequences save the "dirty" FPU registers only.

This works at the initial trap level because all of the registers
get recorded into the top-level FPU save area, and we'll return
to userspace with the FPU disabled so that any FPU use by the user
will take an FPU disabled trap wherein we'll load the registers
back up properly.

But this is not how trap returns from kernel to kernel operate.

The simplest fix for this bug is to always save all FPU register state
for anything other than the top-most FPU save area.

Getting rid of the optimized inner-slot FPU saving code ends up
making VISEntryHalf degenerate into plain VISEntry.

Longer term we need to do something smarter to reinstate the partial
save optimizations.  Perhaps the fundament error is having trap entry
and exit allocate FPU save slots and restore register state.  Instead,
the VISEntry et al. calls should be doing that work.

This bug is about two decades old.

Reported-by: James Y Knight <jyknight@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2015-08-06 19:13:25 -07:00
..
boot sparc: Add "install" target 2014-08-04 20:45:59 -07:00
configs sparc: Set CONFIG_NET=y in defconfigs 2014-09-24 13:38:30 -04:00
crypto crypto: sparc/md5 - use md5 IV MD5_HX instead of their raw value 2015-05-18 12:20:20 +08:00
include sparc64: Fix userspace FPU register corruptions. 2015-08-06 19:13:25 -07:00
kernel RTC for 4.2 2015-06-25 18:55:33 -07:00
lib sparc64: Fix userspace FPU register corruptions. 2015-08-06 19:13:25 -07:00
math-emu arch/sparc/math-emu/math_32.c: drop stray break operator 2014-08-04 20:29:06 -07:00
mm sparc64: Convert BUG_ON to warning 2015-06-25 06:01:02 -07:00
net module: remove mod arg from module_free, rename module_memfree(). 2015-01-20 11:38:33 +10:30
oprofile
power Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc 2014-10-11 20:36:34 -04:00
prom sparc64: Fix register corruption in top-most kernel stack frame during boot. 2014-10-24 09:52:49 -07:00
Kbuild sparc64: Add SHA1 driver making use of the 'sha1' instruction. 2012-08-20 15:08:49 -07:00
Kconfig sparc: time: Replace update_persistent_clock() with CONFIG_RTC_SYSTOHC 2015-06-25 01:13:43 +02:00
Kconfig.debug lib: consolidate DEBUG_STACK_USAGE option 2011-05-25 08:39:54 -07:00
Makefile sparc: Add "install" target 2014-08-04 20:45:59 -07:00