From 06888d571b513cbfc0b41949948def6cb81021b2 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Fri, 28 May 2021 10:53:54 -0700
Subject: [PATCH] drm/amd/display: Avoid HDCP over-read and corruption
Git-commit: 06888d571b513cbfc0b41949948def6cb81021b2
Patch-mainline: v5.14-rc1
References: git-fixes

Instead of reading the desired 5 bytes of the actual target field,
the code was reading 8. This could result in a corrupted value if the
trailing 3 bytes were non-zero, so instead use an appropriately sized
and zero-initialized bounce buffer, and read only 5 bytes before casting
to u64.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c b/drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c
index 43e6f8b17e79..de872e7958b0 100644
--- a/drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c
+++ b/drivers/gpu/drm/amd/display/modules/hdcp/hdcp1_execution.c
@@ -29,8 +29,10 @@ static inline enum mod_hdcp_status validate_bksv(struct mod_hdcp *hdcp)
 {
 	uint64_t n = 0;
 	uint8_t count = 0;
+	u8 bksv[sizeof(n)] = { };
 
-	memcpy(&n, hdcp->auth.msg.hdcp1.bksv, sizeof(uint64_t));
+	memcpy(bksv, hdcp->auth.msg.hdcp1.bksv, sizeof(hdcp->auth.msg.hdcp1.bksv));
+	n = *(uint64_t *)bksv;
 
 	while (n) {
 		count++;
-- 
2.26.2