FAILED: patch "[PATCH] LoongArch: Add spectre boundry for syscall dispatch table" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 0c965d2784fbbd7f8e3b96d875c9cfdf7c00da3d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026042749-impromptu-yeast-b4ca@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 0c965d2784fbbd7f8e3b96d875c9cfdf7c00da3d Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <[email protected]>
Date: Wed, 22 Apr 2026 15:45:12 +0800
Subject: [PATCH] LoongArch: Add spectre boundry for syscall dispatch table

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.

index 1249d82c1cd0..dac435c32743 100644
@@ -9,6 +9,7 @@
 #include <linux/entry-common.h>
 #include <linux/errno.h>
 #include <linux/linkage.h>
+#include <linux/nospec.h>
 #include <linux/objtool.h>
 #include <linux/randomize_kstack.h>
 #include <linux/syscalls.h>

@@ -74,7 +75,7 @@ void noinstr __no_stack_protector do_syscall(struct pt_regs *regs)
 	add_random_kstack_offset();
 
 	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]);
 	}