2021-05-28 17:55:52

by Kees Cook

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

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 <[email protected]>
---
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

2021-06-02 03:50:48

by Alex Deucher

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

On Fri, May 28, 2021 at 1:54 PM Kees Cook <[email protected]> wrote:
>
> 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 <[email protected]>

Applied. Thanks!

> ---
> 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
>