Messages in this thread | | | Subject | Re: [Linux-graphics-maintainer] [PATCH] drm/vmwgfx: Fix potential Spectre v1 | From | Thomas Hellstrom <> | Date | Tue, 21 Aug 2018 10:19:16 +0200 |
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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: stable@vger.kernel.org >> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> >> --- >> 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 <linux/sync_file.h> >> +#include <linux/nospec.h> >> >> #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(&arg.context_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(&arg.context_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-maintainer@vmware.com
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