diff options
| author | Andy Lutomirski <luto@MIT.EDU> | 2011-08-03 09:31:53 -0400 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2011-08-04 16:13:49 -0700 |
| commit | 318f5a2a672152328c9fb4dead504b89ec738a43 (patch) | |
| tree | d37bcc93c8c1b29c057c44dac13148531706631e /arch/x86/include | |
| parent | 5d5791af4c0d4fd32093882357506355c3357503 (diff) | |
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')
| -rw-r--r-- | arch/x86/include/asm/desc.h | 4 | ||||
| -rw-r--r-- | arch/x86/include/asm/paravirt_types.h | 6 | ||||
| -rw-r--r-- | arch/x86/include/asm/ptrace.h | 19 |
3 files changed, 27 insertions, 2 deletions
diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h index 7b439d9aea2a..41935fadfdfc 100644 --- a/arch/x86/include/asm/desc.h +++ b/arch/x86/include/asm/desc.h @@ -27,8 +27,8 @@ static inline void fill_ldt(struct desc_struct *desc, const struct user_desc *in desc->base2 = (info->base_addr & 0xff000000) >> 24; /* - * Don't allow setting of the lm bit. It is useless anyway - * because 64bit system calls require __USER_CS: + * Don't allow setting of the lm bit. It would confuse + * user_64bit_mode and would get overridden by sysret anyway. */ desc->l = 0; } diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h index 82885099c869..96a0f80407b8 100644 --- a/arch/x86/include/asm/paravirt_types.h +++ b/arch/x86/include/asm/paravirt_types.h @@ -41,6 +41,7 @@ #include <asm/desc_defs.h> #include <asm/kmap_types.h> +#include <asm/pgtable_types.h> struct page; struct thread_struct; @@ -63,6 +64,11 @@ struct paravirt_callee_save { struct pv_info { unsigned int kernel_rpl; int shared_kernel_pmd; + +#ifdef CONFIG_X86_64 + u16 extra_user_64bit_cs; /* __USER_CS if none */ +#endif + int paravirt_enabled; const char *name; }; 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 |