[PATCH 6.6.y] LoongArch: Add spectre boundry for syscall dispatch table

[Sasha Levin <sashal@kernel.org>]

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

[ Upstream commit 0c965d2784fbbd7f8e3b96d875c9cfdf7c00da3d ]

The LoongArch syscall number is directly controlled by userspace, but
does not have a array_index_nospec() boundry to prevent access past the
syscall function pointer tables.

Cc: stable@vger.kernel.org
Assisted-by: gkh_clanker_2000
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/loongarch/kernel/syscall.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/kernel/syscall.c b/arch/loongarch/kernel/syscall.c
index b4c5acd7aa3b3..f4e3bd219b1d7 100644
--- a/arch/loongarch/kernel/syscall.c
+++ b/arch/loongarch/kernel/syscall.c
@@ -9,6 +9,7 @@
 #include <linux/entry-common.h>
 #include <linux/errno.h>
 #include <linux/linkage.h>
+#include <linux/nospec.h>
 #include <linux/syscalls.h>
 #include <linux/unistd.h>
 
@@ -55,7 +56,7 @@ void noinstr do_syscall(struct pt_regs *regs)
 	nr = syscall_enter_from_user_mode(regs, nr);
 
 	if (nr < NR_syscalls) {
-		syscall_fn = sys_call_table[nr];
+		syscall_fn = sys_call_table[array_index_nospec(nr, NR_syscalls)];
 		regs->regs[4] = syscall_fn(regs->orig_a0, regs->regs[5], regs->regs[6],
 					   regs->regs[7], regs->regs[8], regs->regs[9]);
 	}
-- 
2.53.0