ARC: entry: fix off-by-one error in syscall number validation

stable inclusion
from stable-5.10.38
commit af9e5364c617d25f34d11c90f6bc7e8f16c63804
bugzilla: 51875
CVE: NA

--------------------------------

commit 3433adc8 upstream.

We have NR_syscall syscalls from [0 .. NR_syscall-1].
However the check for invalid syscall number is "> NR_syscall" as
opposed to >=. This off-by-one error erronesously allows "NR_syscall"
to be treated as valid syscall causeing out-of-bounds access into
syscall-call table ensuing a crash (holes within syscall table have a
invalid-entry handler but this is beyond the array implementing the
table).

This problem showed up on v5.6 kernel when testing glibc 2.33 (v5.10
kernel capable, includng faccessat2 syscall 439). The v5.6 kernel has
NR_syscalls=439 (0 to 438). Due to the bug, 439 passed by glibc was
not handled as -ENOSYS but processed leading to a crash.

Link: https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/48Reported-by: NShahab Vahedi <shahab@synopsys.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NVineet Gupta <vgupta@synopsys.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/arc/kernel/entry.S

@@ -177,7 +177,7 @@ tracesys:
 
 	; Do the Sys Call as we normally would.
 	; Validate the Sys Call number
-	cmp     r8,  NR_syscalls
+	cmp     r8,  NR_syscalls - 1
 	mov.hi  r0, -ENOSYS
 	bhi     tracesys_exit
 
@@ -255,7 +255,7 @@ ENTRY(EV_Trap)
 	;============ Normal syscall case
 
 	; syscall num shd not exceed the total system calls avail
-	cmp     r8,  NR_syscalls
+	cmp     r8,  NR_syscalls - 1
 	mov.hi  r0, -ENOSYS
 	bhi     .Lret_from_system_call