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authorAndy Lutomirski <luto@MIT.EDU>2011-08-03 17:31:53 +0400
committerH. Peter Anvin <hpa@linux.intel.com>2011-08-05 03:13:49 +0400
commit318f5a2a672152328c9fb4dead504b89ec738a43 (patch)
treed37bcc93c8c1b29c057c44dac13148531706631e /arch/x86/include/asm/ptrace.h
parent5d5791af4c0d4fd32093882357506355c3357503 (diff)
downloadlinux-318f5a2a672152328c9fb4dead504b89ec738a43.tar.xz
x86-64: Add user_64bit_mode paravirt op
Three places in the kernel assume that the only long mode CPL 3 selector is __USER_CS. This is not true on Xen -- Xen's sysretq changes cs to the magic value 0xe033. Two of the places are corner cases, but as of "x86-64: Improve vsyscall emulation CS and RIP handling" (c9712944b2a12373cb6ff8059afcfb7e826a6c54), vsyscalls will segfault if called with Xen's extra CS selector. This causes a panic when older init builds die. It seems impossible to make Xen use __USER_CS reliably without taking a performance hit on every system call, so this fixes the tests instead with a new paravirt op. It's a little ugly because ptrace.h can't include paravirt.h. Signed-off-by: Andy Lutomirski <luto@mit.edu> Link: http://lkml.kernel.org/r/f4fcb3947340d9e96ce1054a432f183f9da9db83.1312378163.git.luto@mit.edu Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch/x86/include/asm/ptrace.h')
-rw-r--r--arch/x86/include/asm/ptrace.h19
1 files changed, 19 insertions, 0 deletions
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 94e7618fcac8..35664547125b 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -131,6 +131,9 @@ struct pt_regs {
#ifdef __KERNEL__
#include <linux/init.h>
+#ifdef CONFIG_PARAVIRT
+#include <asm/paravirt_types.h>
+#endif
struct cpuinfo_x86;
struct task_struct;
@@ -187,6 +190,22 @@ static inline int v8086_mode(struct pt_regs *regs)
#endif
}
+#ifdef CONFIG_X86_64
+static inline bool user_64bit_mode(struct pt_regs *regs)
+{
+#ifndef CONFIG_PARAVIRT
+ /*
+ * On non-paravirt systems, this is the only long mode CPL 3
+ * selector. We do not allow long mode selectors in the LDT.
+ */
+ return regs->cs == __USER_CS;
+#else
+ /* Headers are too twisted for this to go in paravirt.h. */
+ return regs->cs == __USER_CS || regs->cs == pv_info.extra_user_64bit_cs;
+#endif
+}
+#endif
+
/*
* X86_32 CPUs don't save ss and esp if the CPU is already in kernel mode
* when it traps. The previous stack will be directly underneath the saved