linux/arch/um/include
Jeff Dike 2f56debd77 uml: fix FP register corruption
Commit ee3d9bd4de ("uml: simplify SIGSEGV
handling"), while greatly simplifying the kernel SIGSEGV handler that
runs in the process address space, introduced a bug which corrupts FP
state in the process.

Previously, the SIGSEGV handler called the sigreturn system call by hand - it
couldn't return through the restorer provided to it because that could try to
call the libc restorer which likely wouldn't exist in the process address
space.  So, it blocked off some signals, including SIGUSR1, on entry to the
SIGSEGV handler, queued a SIGUSR1 to itself, and invoked sigreturn.  The
SIGUSR1 was delivered, and was visible to the UML kernel after sigreturn
finished.

The commit eliminated the signal masking and the call to sigreturn.  The
handler simply hits itself with a SIGTRAP to let the UML kernel know that it
is finished.  UML then restores the process registers, which effectively
longjmps the process out of the signal handler, skipping sigreturn's restoring
of register state and the signal mask.

The bug is that the host apparently sets used_fp to 0 when it saves the
process FP state in the sigcontext on the process signal stack.  Thus, when
the process is longjmped out of the handler, its FP state is corrupt because
it wasn't saved on the context switch to the UML kernel.

This manifested itself as sleep hanging.  For some reason, sleep uses floating
point in order to calculate the sleep interval.  When a page fault corrupts
its FP state, it is faked into essentially sleeping forever.

This patch saves the FP state before entering the SIGSEGV handler and restores
it afterwards.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-02-23 17:12:15 -08:00
..
skas uml: delete some unused headers 2008-02-05 09:44:26 -08:00
sysdep-i386 uml: fix FP register corruption 2008-02-23 17:12:15 -08:00
sysdep-ia64 [PATCH] uml: S390 preparation, abstract host page fault data 2005-05-05 16:36:36 -07:00
sysdep-ppc Remove all inclusions of <linux/config.h> 2006-10-04 03:38:54 -04:00
sysdep-x86_64 uml: fix FP register corruption 2008-02-23 17:12:15 -08:00
aio.h [PATCH] uml: revert block driver use of host AIO 2005-10-12 08:22:26 -07:00
arch.h uml: further bugs.c tidying 2008-02-05 09:44:25 -08:00
as-layout.h uml: runtime host VMSPLIT detection 2008-02-08 09:22:42 -08:00
chan_kern.h uml: handle errors on opening host side of consoles 2007-07-16 09:05:38 -07:00
chan_user.h uml: fix URLs in Kconfig and help strings 2008-02-05 09:44:25 -08:00
common-offsets.h uml: cover stubs with a VMA 2008-02-05 09:44:29 -08:00
elf_user.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
frame_kern.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
init.h uml: arch/um/include/init.h needs a definition of __used 2008-02-05 09:44:24 -08:00
initrd.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
irq_kern.h IRQ: Use the new typedef for interrupt handler function pointers 2006-10-09 12:19:47 +01:00
irq_user.h uml: miscellaneous code cleanups 2008-02-05 09:44:29 -08:00
kern.h [PATCH] uml: fix declaration of exit() 2006-03-27 08:44:37 -08:00
kern_util.h uml: get rid of syscall counters 2008-02-05 09:44:30 -08:00
line.h [PATCH] uml: fix previous console locking 2007-02-11 10:51:22 -08:00
longjmp.h [PATCH] uml: make UML_SETJMP always safe 2006-10-11 11:14:20 -07:00
mconsole.h uml: remove os_* usage from userspace files 2007-10-16 09:43:06 -07:00
mconsole_kern.h [PATCH] uml: console whitespace and comment tidying 2007-02-11 10:51:21 -08:00
mem.h uml: remove __u64 usage from physical memory subsystem 2007-10-16 09:43:05 -07:00
mem_kern.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
mem_user.h uml: SMP locking commentary 2008-02-05 09:44:30 -08:00
net_kern.h uml: network driver MTU cleanups 2007-10-16 09:43:08 -07:00
net_user.h uml: network driver MTU cleanups 2007-10-16 09:43:08 -07:00
os.h uml: runtime host VMSPLIT detection 2008-02-08 09:22:42 -08:00
process.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
ptrace_user.h uml: style fixes in arch/um/sys-x86_64 2008-02-05 09:44:31 -08:00
registers.h uml: fix FP register corruption 2008-02-23 17:12:15 -08:00
sigcontext.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sigio.h [PATCH] uml: SIGIO formatting fixes 2007-02-11 10:51:23 -08:00
skas_ptrace.h [PATCH] uml: header and code cleanup 2005-05-05 16:36:39 -07:00
skas_ptregs.h [PATCH] uml makefiles sanitized 2005-09-29 08:46:26 -07:00
syscall.h [PATCH] uml: system call path cleanup 2005-09-05 00:06:23 -07:00
sysrq.h [PATCH] uml: stack dump fix 2005-05-28 16:46:13 -07:00
task.h uml: remove code made redundant by CHOOSE_MODE removal 2007-10-16 09:43:05 -07:00
tlb.h uml: clean up tlb flush path 2007-10-16 09:43:06 -07:00
ubd_user.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
um_malloc.h uml: Eliminate kernel allocator wrappers 2007-07-16 09:05:38 -07:00
um_mmu.h uml: fix mm_context memory leak 2008-02-08 09:22:43 -08:00
um_uaccess.h uml: header untangling 2008-02-05 09:44:28 -08:00
user.h uml: fix build for !CONFIG_PRINTK 2007-11-14 18:45:43 -08:00