[PATCH] drm/amd/display: Avoid HDCP over-read and corruption

[Kees Cook]

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 <keesc...@chromium.org>
---
 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 2cbd931363bd..6d26d9c63ab2 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++;
-- 
2.25.1