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x32: Handle the x32 system call flag 

x32 shares most system calls with x86-64, but unfortunately some
subsystem (the input subsystem is the chief offender) which require
is_compat() when operating with a 32-bit userspace.  The input system
actually has text files in sysfs whose meaning is dependent on
sizeof(long) in userspace!

We could solve this by having two completely disjoint system call
tables; requiring that each system call be duplicated.  This patch
takes a different approach: we add a flag to the system call number;
this flag doesn't affect the system call dispatch but requests compat
treatment from affected subsystems for the duration of the system call.

The change of cmpq to cmpl is safe since it immediately follows the
and.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
H. Peter Anvin 2012-02-19 07:56:26 -08:00
parent 9d3897630e
commit fca460f95e
4 changed files with 31 additions and 4 deletions
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13
arch/x86/include/asm/compat.h
View File

@ -7,6 +7,7 @@
#include <linux/types.h>
#include <linux/sched.h>
#include <asm/user32.h>
#include <asm/unistd.h>
#define COMPAT_USER_HZ 100
#define COMPAT_UTS_MACHINE "i686\0\0"
@ -212,9 +213,17 @@ static inline void __user *arch_compat_alloc_user_space(long len)
return (void __user *)regs->sp - len;
}
static inline int is_compat_task(void)
static inline bool is_compat_task(void)
{
return current_thread_info()->status & TS_COMPAT;
#ifdef CONFIG_IA32_EMULATION
if (current_thread_info()->status & TS_COMPAT)
return true;
#endif
#ifdef CONFIG_X86_X32_ABI
if (task_pt_regs(current)->orig_ax & __X32_SYSCALL_BIT)
return true;
#endif
return false;
}
#endif /* _ASM_X86_COMPAT_H */

5
arch/x86/include/asm/syscall.h
View File

@ -16,6 +16,7 @@
#include <linux/sched.h>
#include <linux/err.h>
#include <asm/asm-offsets.h> /* For NR_syscalls */
#include <asm/unistd.h>
extern const unsigned long sys_call_table[];
@ -26,13 +27,13 @@ extern const unsigned long sys_call_table[];
*/
static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
{
return regs->orig_ax;
return regs->orig_ax & __SYSCALL_MASK;
}
static inline void syscall_rollback(struct task_struct *task,
struct pt_regs *regs)
{
regs->ax = regs->orig_ax;
regs->ax = regs->orig_ax & __SYSCALL_MASK;
}
static inline long syscall_get_error(struct task_struct *task,

7
arch/x86/include/asm/unistd.h
View File

@ -5,6 +5,13 @@
#define __X32_SYSCALL_BIT 0x40000000
#ifdef __KERNEL__
# ifdef CONFIG_X86_X32_ABI
# define __SYSCALL_MASK (~(__X32_SYSCALL_BIT))
# else
# define __SYSCALL_MASK (~0)
# endif
# ifdef CONFIG_X86_32
# include <asm/unistd_32.h>

10
arch/x86/kernel/entry_64.S
View File

@ -482,7 +482,12 @@ GLOBAL(system_call_after_swapgs)
testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)
jnz tracesys
system_call_fastpath:
#if __SYSCALL_MASK == ~0
cmpq $__NR_syscall_max,%rax
#else
andl $__SYSCALL_MASK,%eax
cmpl $__NR_syscall_max,%eax
#endif
ja badsys
movq %r10,%rcx
call *sys_call_table(,%rax,8) # XXX: rip relative
@ -596,7 +601,12 @@ tracesys:
*/
LOAD_ARGS ARGOFFSET, 1
RESTORE_REST
#if __SYSCALL_MASK == ~0
cmpq $__NR_syscall_max,%rax
#else
andl $__SYSCALL_MASK,%eax
cmpl $__NR_syscall_max,%eax
#endif
ja int_ret_from_sys_call /* RAX(%rsp) set to -ENOSYS above */
movq %r10,%rcx /* fixup for C */
call *sys_call_table(,%rax,8)