x86-64, compat: Test %rax for the syscall number, not %eax

On 64 bits, we always, by necessity, jump through the system call
table via %rax.  For 32-bit system calls, in theory the system call
number is stored in %eax, and the code was testing %eax for a valid
system call number.  At one point we loaded the stored value back from
the stack to enforce zero-extension, but that was removed in checkin
d4d67150165df8bf1cc05e532f6efca96f907cab.  An actual 32-bit process
will not be able to introduce a non-zero-extended number, but it can
happen via ptrace.

Instead of re-introducing the zero-extension, test what we are
actually going to use, i.e. %rax.  This only adds a handful of REX
prefixes to the code.

Reported-by: Ben Hawkes <hawkes@sota.gen.nz>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: <stable@kernel.org>
Cc: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 7 insertions, 7 deletions

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index b86feabed69b..84e3a4ef9719 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -153,7 +153,7 @@ ENTRY(ia32_sysenter_target)
         testl  $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%r10)
         CFI_REMEMBER_STATE
         jnz  sysenter_tracesys
-        cmpl    $(IA32_NR_syscalls-1),%eax
+        cmpq    $(IA32_NR_syscalls-1),%rax
         ja      ia32_badsys
 sysenter_do_call:
         IA32_ARG_FIXUP
@@ -195,7 +195,7 @@ sysexit_from_sys_call:
         movl $AUDIT_ARCH_I386,%edi      /* 1st arg: audit arch */
         call audit_syscall_entry
         movl RAX-ARGOFFSET(%rsp),%eax   /* reload syscall number */
-        cmpl $(IA32_NR_syscalls-1),%eax
+        cmpq $(IA32_NR_syscalls-1),%rax
         ja ia32_badsys
         movl %ebx,%edi                  /* reload 1st syscall arg */
         movl RCX-ARGOFFSET(%rsp),%esi   /* reload 2nd syscall arg */
@@ -248,7 +248,7 @@ sysenter_tracesys:
         call    syscall_trace_enter
         LOAD_ARGS32 ARGOFFSET  /* reload args from stack in case ptrace changed it */
         RESTORE_REST
-        cmpl    $(IA32_NR_syscalls-1),%eax
+        cmpq    $(IA32_NR_syscalls-1),%rax
         ja      int_ret_from_sys_call /* sysenter_tracesys has set RAX(%rsp) */
         jmp     sysenter_do_call
         CFI_ENDPROC
@@ -314,7 +314,7 @@ ENTRY(ia32_cstar_target)
         testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%r10)
         CFI_REMEMBER_STATE
         jnz   cstar_tracesys
-        cmpl $IA32_NR_syscalls-1,%eax
+        cmpq $IA32_NR_syscalls-1,%rax
         ja  ia32_badsys
 cstar_do_call:
         IA32_ARG_FIXUP 1
@@ -367,7 +367,7 @@ cstar_tracesys:
         LOAD_ARGS32 ARGOFFSET, 1  /* reload args from stack in case ptrace changed it */
         RESTORE_REST
         xchgl %ebp,%r9d
-        cmpl $(IA32_NR_syscalls-1),%eax
+        cmpq $(IA32_NR_syscalls-1),%rax
         ja int_ret_from_sys_call /* cstar_tracesys has set RAX(%rsp) */
         jmp cstar_do_call
 END(ia32_cstar_target)
@@ -425,7 +425,7 @@ ENTRY(ia32_syscall)
         orl   $TS_COMPAT,TI_status(%r10)
         testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%r10)
         jnz ia32_tracesys
-        cmpl $(IA32_NR_syscalls-1),%eax
+        cmpq $(IA32_NR_syscalls-1),%rax
         ja ia32_badsys
 ia32_do_call:
         IA32_ARG_FIXUP
@@ -444,7 +444,7 @@ ia32_tracesys:
         call syscall_trace_enter
         LOAD_ARGS32 ARGOFFSET  /* reload args from stack in case ptrace changed it */
         RESTORE_REST
-        cmpl $(IA32_NR_syscalls-1),%eax
+        cmpq $(IA32_NR_syscalls-1),%rax
         ja  int_ret_from_sys_call       /* ia32_tracesys has set RAX(%rsp) */
         jmp ia32_do_call
 END(ia32_syscall)