2f56debd77
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>
79 lines
1.7 KiB
C
79 lines
1.7 KiB
C
/*
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* Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
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* Licensed under the GPL
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*/
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#ifndef __SYSDEP_I386_PTRACE_USER_H__
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#define __SYSDEP_I386_PTRACE_USER_H__
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#include <sys/ptrace.h>
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#include <linux/ptrace.h>
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#include <asm/ptrace.h>
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#include "user_constants.h"
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#define PT_OFFSET(r) ((r) * sizeof(long))
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#define PT_SYSCALL_NR(regs) ((regs)[ORIG_EAX])
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#define PT_SYSCALL_NR_OFFSET PT_OFFSET(ORIG_EAX)
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#define PT_SYSCALL_ARG1_OFFSET PT_OFFSET(EBX)
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#define PT_SYSCALL_ARG2_OFFSET PT_OFFSET(ECX)
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#define PT_SYSCALL_ARG3_OFFSET PT_OFFSET(EDX)
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#define PT_SYSCALL_ARG4_OFFSET PT_OFFSET(ESI)
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#define PT_SYSCALL_ARG5_OFFSET PT_OFFSET(EDI)
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#define PT_SYSCALL_ARG6_OFFSET PT_OFFSET(EBP)
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#define PT_SYSCALL_RET_OFFSET PT_OFFSET(EAX)
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#define REGS_SYSCALL_NR EAX /* This is used before a system call */
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#define REGS_SYSCALL_ARG1 EBX
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#define REGS_SYSCALL_ARG2 ECX
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#define REGS_SYSCALL_ARG3 EDX
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#define REGS_SYSCALL_ARG4 ESI
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#define REGS_SYSCALL_ARG5 EDI
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#define REGS_SYSCALL_ARG6 EBP
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#define REGS_IP_INDEX EIP
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#define REGS_SP_INDEX UESP
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#define PT_IP_OFFSET PT_OFFSET(EIP)
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#define PT_IP(regs) ((regs)[EIP])
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#define PT_SP_OFFSET PT_OFFSET(UESP)
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#define PT_SP(regs) ((regs)[UESP])
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#define FP_SIZE ((HOST_XFP_SIZE > HOST_FP_SIZE) ? HOST_XFP_SIZE : HOST_FP_SIZE)
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#ifndef FRAME_SIZE
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#define FRAME_SIZE (17)
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#endif
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#define FRAME_SIZE_OFFSET (FRAME_SIZE * sizeof(unsigned long))
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#define FP_FRAME_SIZE (27)
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#define FPX_FRAME_SIZE (128)
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#ifdef PTRACE_GETREGS
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#define UM_HAVE_GETREGS
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#endif
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#ifdef PTRACE_SETREGS
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#define UM_HAVE_SETREGS
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#endif
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#ifdef PTRACE_GETFPREGS
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#define UM_HAVE_GETFPREGS
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#endif
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#ifdef PTRACE_SETFPREGS
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#define UM_HAVE_SETFPREGS
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#endif
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#ifdef PTRACE_GETFPXREGS
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#define UM_HAVE_GETFPXREGS
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#endif
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#ifdef PTRACE_SETFPXREGS
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#define UM_HAVE_SETFPXREGS
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#endif
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#endif
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