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>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 3fe8239fd8fb..a17b34216971 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -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)