From 2f56debd77a8f52f1ac1d3c3d89cc7ce5e083230 Mon Sep 17 00:00:00 2001 From: Jeff Dike Date: Sat, 23 Feb 2008 15:23:49 -0800 Subject: [PATCH] uml: fix FP register corruption Commit ee3d9bd4de1ed93d2a7ee41c331ed30a1c7b8acd ("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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/um/include/registers.h | 2 ++ arch/um/include/sysdep-i386/ptrace_user.h | 3 +++ arch/um/include/sysdep-x86_64/ptrace_user.h | 3 +++ arch/um/os-Linux/skas/process.c | 15 +++++++++++++++ arch/um/os-Linux/sys-i386/registers.c | 16 ++++++++++++++++ arch/um/os-Linux/sys-x86_64/registers.c | 10 ++++++++++ 6 files changed, 49 insertions(+) diff --git a/arch/um/include/registers.h b/arch/um/include/registers.h index 9ea1ae3c8f..b0b4589e0e 100644 --- a/arch/um/include/registers.h +++ b/arch/um/include/registers.h @@ -18,5 +18,7 @@ extern int restore_registers(int pid, struct uml_pt_regs *regs); extern int init_registers(int pid); extern void get_safe_registers(unsigned long *regs); extern unsigned long get_thread_reg(int reg, jmp_buf *buf); +extern int get_fp_registers(int pid, unsigned long *regs); +extern int put_fp_registers(int pid, unsigned long *regs); #endif diff --git a/arch/um/include/sysdep-i386/ptrace_user.h b/arch/um/include/sysdep-i386/ptrace_user.h index 899aa4b2a7..75650723c3 100644 --- a/arch/um/include/sysdep-i386/ptrace_user.h +++ b/arch/um/include/sysdep-i386/ptrace_user.h @@ -9,6 +9,7 @@ #include #include #include +#include "user_constants.h" #define PT_OFFSET(r) ((r) * sizeof(long)) @@ -40,6 +41,8 @@ #define PT_SP_OFFSET PT_OFFSET(UESP) #define PT_SP(regs) ((regs)[UESP]) +#define FP_SIZE ((HOST_XFP_SIZE > HOST_FP_SIZE) ? HOST_XFP_SIZE : HOST_FP_SIZE) + #ifndef FRAME_SIZE #define FRAME_SIZE (17) #endif diff --git a/arch/um/include/sysdep-x86_64/ptrace_user.h b/arch/um/include/sysdep-x86_64/ptrace_user.h index 4cd61a852f..45c0bd881c 100644 --- a/arch/um/include/sysdep-x86_64/ptrace_user.h +++ b/arch/um/include/sysdep-x86_64/ptrace_user.h @@ -12,6 +12,7 @@ #include #include #undef __FRAME_OFFSETS +#include "user_constants.h" #define PT_INDEX(off) ((off) / sizeof(unsigned long)) @@ -69,6 +70,8 @@ #define REGS_IP_INDEX PT_INDEX(RIP) #define REGS_SP_INDEX PT_INDEX(RSP) +#define FP_SIZE (HOST_FP_SIZE) + #endif /* diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c index b14829469f..1e8cba6550 100644 --- a/arch/um/os-Linux/skas/process.c +++ b/arch/um/os-Linux/skas/process.c @@ -115,6 +115,14 @@ void get_skas_faultinfo(int pid, struct faultinfo * fi) sizeof(struct ptrace_faultinfo)); } else { + unsigned long fpregs[FP_SIZE]; + + err = get_fp_registers(pid, fpregs); + if (err < 0) { + printk(UM_KERN_ERR "save_fp_registers returned %d\n", + err); + fatal_sigsegv(); + } err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV); if (err) { printk(UM_KERN_ERR "Failed to continue stub, pid = %d, " @@ -128,6 +136,13 @@ void get_skas_faultinfo(int pid, struct faultinfo * fi) * the stub stack page. We just have to copy it. */ memcpy(fi, (void *)current_stub_stack(), sizeof(*fi)); + + err = put_fp_registers(pid, fpregs); + if (err < 0) { + printk(UM_KERN_ERR "put_fp_registers returned %d\n", + err); + fatal_sigsegv(); + } } } diff --git a/arch/um/os-Linux/sys-i386/registers.c b/arch/um/os-Linux/sys-i386/registers.c index f74d853a0e..b613473b3e 100644 --- a/arch/um/os-Linux/sys-i386/registers.c +++ b/arch/um/os-Linux/sys-i386/registers.c @@ -56,6 +56,22 @@ unsigned long get_thread_reg(int reg, jmp_buf *buf) int have_fpx_regs = 1; +int get_fp_registers(int pid, unsigned long *regs) +{ + if (have_fpx_regs) + return save_fpx_registers(pid, regs); + else + return save_fp_registers(pid, regs); +} + +int put_fp_registers(int pid, unsigned long *regs) +{ + if (have_fpx_regs) + return restore_fpx_registers(pid, regs); + else + return restore_fp_registers(pid, regs); +} + void arch_init_registers(int pid) { unsigned long fpx_regs[HOST_XFP_SIZE]; diff --git a/arch/um/os-Linux/sys-x86_64/registers.c b/arch/um/os-Linux/sys-x86_64/registers.c index a375853337..594d97ad02 100644 --- a/arch/um/os-Linux/sys-x86_64/registers.c +++ b/arch/um/os-Linux/sys-x86_64/registers.c @@ -40,3 +40,13 @@ unsigned long get_thread_reg(int reg, jmp_buf *buf) return 0; } } + +int get_fp_registers(int pid, unsigned long *regs) +{ + return save_fp_registers(pid, regs); +} + +int put_fp_registers(int pid, unsigned long *regs) +{ + return restore_fp_registers(pid, regs); +} -- 2.39.5