Patch "drm/amd/display: Avoid HDCP over-read and corruption" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-amd-display-avoid-hdcp-over-read-and-corruption.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 81d68f86bdad2dcbcb4908bad5f1b03657e02505
Author: Kees Cook <keescook@xxxxxxxxxxxx>
Date:   Fri May 28 10:53:54 2021 -0700

    drm/amd/display: Avoid HDCP over-read and corruption
    
    [ Upstream commit 06888d571b513cbfc0b41949948def6cb81021b2 ]
    
    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@xxxxxxxxxxxx>
    Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

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 f244b72e74e0..53eab2b8e2c8 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++;