Re: [Linux-graphics-maintainer] [PATCH] drm/vmwgfx: Fix potential Spectre v1
Hi all,
On 8/21/18 3:19 AM, Thomas Hellstrom wrote:
>>> #include "vmwgfx_drv.h"
>>> #include "vmwgfx_reg.h"
>>> @@ -4520,8 +4521,10 @@ int vmw_execbuf_ioctl(struct drm_device *dev,
>>> unsigned long data,
>>> return -EINVAL;
>>> }
>>>
>>> - if (arg.version > 1 &&
>>> - copy_from_user(_handle,
>>> + if (arg.version >= ARRAY_SIZE(copy_offset))
>>> + return -EFAULT;
>
> I must admit my understanding of spectre workings in this case is limited,
> but why do you need to compare
> arg.version against ARRAY_SIZE here, when it is already checked against
> DRM_VMW_EXECBUF_VERSION earlier?
>
Oh, I wasn't aware of the value in DRM_VMW_EXECBUF_VERSION. But as arg.version
is used to index copy_offset,
it is safer to compare its value against the actual size of copy_offset.
So, what do you think if I replace DRM_VMW_EXECBUF_VERSION with ARRAY_SIZE
instead of adding a new check
against ARRAY_SIZE?
Something like:
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
index 1f13457..3ef9f7b 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
@@ -25,6 +25,7 @@
*
**/
#include
+#include
#include "vmwgfx_drv.h"
#include "vmwgfx_reg.h"
@@ -4514,11 +4515,12 @@ int vmw_execbuf_ioctl(struct drm_device *dev, unsigned
long data,
* arg.version.
*/
- if (unlikely(arg.version > DRM_VMW_EXECBUF_VERSION ||
+ if (unlikely(arg.version > ARRAY_SIZE(copy_offset) ||
arg.version == 0)) {
DRM_ERROR("Incorrect execbuf version.\n");
return -EINVAL;
}
+ arg.version = array_index_nospec(arg.version, ARRAY_SIZE(copy_offset));
if (arg.version > 1 &&
copy_from_user(_handle,
>
>
>>> + arg.version = array_index_nospec(arg.version,
>>> ARRAY_SIZE(copy_offset));
>>> + if (copy_from_user(_handle,
>>> (void __user *) (data + copy_offset[0]),
>>> copy_offset[arg.version - 1] -
>>> copy_offset[0]) != 0)
>
> Similarly, we want to perform this copy iff arg.version > 1. Why did you
> remove that check?
>
Yeah, this check must remain in place. I will add it back and send v2.
Thanks for the feedback!
--
Gustavo
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Re: [Linux-graphics-maintainer] [PATCH] drm/vmwgfx: Fix potential Spectre v1
On 08/20/2018 10:53 PM, Deepak Singh Rawat wrote: Looks good to me based on my limited understanding. Thomas/Sinclair can could you please review and then we can include this in drm-fixes. Thanks, Deepak arg.version is indirectly controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability. This issue was detected with the help of Smatch: drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c:4526 vmw_execbuf_ioctl() warn: potential spectre issue 'copy_offset' [w] Fix this by sanitizing arg.version before using it to index copy_offset Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1]. [1] Cc: sta...@vger.kernel.org Signed-off-by: Gustavo A. R. Silva --- drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c | 7 +-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c index 1f13457..ad91c6e 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c @@ -25,6 +25,7 @@ * ** / #include +#include #include "vmwgfx_drv.h" #include "vmwgfx_reg.h" @@ -4520,8 +4521,10 @@ int vmw_execbuf_ioctl(struct drm_device *dev, unsigned long data, return -EINVAL; } - if (arg.version > 1 && - copy_from_user(_handle, + if (arg.version >= ARRAY_SIZE(copy_offset)) + return -EFAULT; I must admit my understanding of spectre workings in this case is limited, but why do you need to compare arg.version against ARRAY_SIZE here, when it is already checked against DRM_VMW_EXECBUF_VERSION earlier? + arg.version = array_index_nospec(arg.version, ARRAY_SIZE(copy_offset)); + if (copy_from_user(_handle, (void __user *) (data + copy_offset[0]), copy_offset[arg.version - 1] - copy_offset[0]) != 0) Similarly, we want to perform this copy iff arg.version > 1. Why did you remove that check? Thanks, Thomas -- 2.7.4 ___ Sent to linux-graphics-maintai...@vmware.com ___ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
RE: [Linux-graphics-maintainer] [PATCH] drm/vmwgfx: Fix potential Spectre v1
Looks good to me based on my limited understanding. Thomas/Sinclair can could you please review and then we can include this in drm-fixes. Thanks, Deepak > > arg.version is indirectly controlled by user-space, hence leading to > a potential exploitation of the Spectre variant 1 vulnerability. > > This issue was detected with the help of Smatch: > > drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c:4526 vmw_execbuf_ioctl() > warn: > potential spectre issue 'copy_offset' [w] > > Fix this by sanitizing arg.version before using it to index copy_offset > > Notice that given that speculation windows are large, the policy is > to kill the speculation on the first load and not worry if it can be > completed with a dependent load/store [1]. > > [1] > https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmarc.i > nfo%2F%3Fl%3Dlinux- > kernel%26m%3D152449131114778%26w%3D2data=02%7C01%7Clinux- > graphics- > maintainer%40vmware.com%7Cf010b707b8ef4896c1a908d603aebcc6%7Cb39 > 138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636700446365603728 > sdata=0D8lnUScxOmCCWXLHh8Otc3o%2F1yF1SxgGwIklRdMlXY%3Dre > served=0 > > Cc: sta...@vger.kernel.org > Signed-off-by: Gustavo A. R. Silva > --- > drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c | 7 +-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c > b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c > index 1f13457..ad91c6e 100644 > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c > @@ -25,6 +25,7 @@ > * > > ** > / > #include > +#include > > #include "vmwgfx_drv.h" > #include "vmwgfx_reg.h" > @@ -4520,8 +4521,10 @@ int vmw_execbuf_ioctl(struct drm_device *dev, > unsigned long data, > return -EINVAL; > } > > - if (arg.version > 1 && > - copy_from_user(_handle, > + if (arg.version >= ARRAY_SIZE(copy_offset)) > + return -EFAULT; > + arg.version = array_index_nospec(arg.version, > ARRAY_SIZE(copy_offset)); > + if (copy_from_user(_handle, > (void __user *) (data + copy_offset[0]), > copy_offset[arg.version - 1] - > copy_offset[0]) != 0) > -- > 2.7.4 > > ___ > Sent to linux-graphics-maintai...@vmware.com ___ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
[PATCH] drm/vmwgfx: Fix potential Spectre v1
arg.version is indirectly controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability. This issue was detected with the help of Smatch: drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c:4526 vmw_execbuf_ioctl() warn: potential spectre issue 'copy_offset' [w] Fix this by sanitizing arg.version before using it to index copy_offset Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1]. [1] https://marc.info/?l=linux-kernel=152449131114778=2 Cc: sta...@vger.kernel.org Signed-off-by: Gustavo A. R. Silva --- drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c | 7 +-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c index 1f13457..ad91c6e 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c @@ -25,6 +25,7 @@ * **/ #include +#include #include "vmwgfx_drv.h" #include "vmwgfx_reg.h" @@ -4520,8 +4521,10 @@ int vmw_execbuf_ioctl(struct drm_device *dev, unsigned long data, return -EINVAL; } - if (arg.version > 1 && - copy_from_user(_handle, + if (arg.version >= ARRAY_SIZE(copy_offset)) + return -EFAULT; + arg.version = array_index_nospec(arg.version, ARRAY_SIZE(copy_offset)); + if (copy_from_user(_handle, (void __user *) (data + copy_offset[0]), copy_offset[arg.version - 1] - copy_offset[0]) != 0) -- 2.7.4 ___ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
