From 271208ee5e335cb1ad280d22784940daf7ddf820 Mon Sep 17 00:00:00 2001
From: Nathan Lynch <nathanl@linux.ibm.com>
Date: Mon, 6 Mar 2023 15:33:41 -0600
Subject: [PATCH] powerpc/rtas: use memmove for potentially overlapping buffer
 copy

References: bsc#1065729
Patch-mainline: v6.4-rc1
Git-commit: 271208ee5e335cb1ad280d22784940daf7ddf820

Using memcpy() isn't safe when buf is identical to rtas_err_buf, which
can happen during boot before slab is up. Full context which may not
be obvious from the diff:

	if (altbuf) {
		buf = altbuf;
	} else {
		buf = rtas_err_buf;
		if (slab_is_available())
			buf = kmalloc(RTAS_ERROR_LOG_MAX, GFP_ATOMIC);
	}
	if (buf)
		memcpy(buf, rtas_err_buf, RTAS_ERROR_LOG_MAX);

This was found by inspection and I'm not aware of it causing problems
in practice. It appears to have been introduced by commit
033ef338b6e0 ("powerpc: Merge rtas.c into arch/powerpc/kernel"); the
old ppc64 version of this code did not have this problem.

Use memmove() instead.

Fixes: 033ef338b6e0 ("powerpc: Merge rtas.c into arch/powerpc/kernel")
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230220-rtas-queue-for-6-4-v1-2-010e4416f13f@linux.ibm.com
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/kernel/rtas.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 31175b34856a..9256cfaa8b6f 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -981,7 +981,7 @@ static char *__fetch_rtas_last_error(char *altbuf)
 				buf = kmalloc(RTAS_ERROR_LOG_MAX, GFP_ATOMIC);
 		}
 		if (buf)
-			memcpy(buf, rtas_err_buf, RTAS_ERROR_LOG_MAX);
+			memmove(buf, rtas_err_buf, RTAS_ERROR_LOG_MAX);
 	}
 
 	return buf;
-- 
2.40.0