| Message ID | 20230103234948.1218393-1-robdclark@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/i915: Fix potential context UAFs | expand |
On 03/01/2023 23:49, Rob Clark wrote: > From: Rob Clark <robdclark@chromium.org> > > gem_context_register() makes the context visible to userspace, and which > point a separate thread can trigger the I915_GEM_CONTEXT_DESTROY ioctl. > So we need to ensure that nothing uses the ctx ptr after this. And we > need to ensure that adding the ctx to the xarray is the *last* thing > that gem_context_register() does with the ctx pointer. Any backtraces from oopses or notes on how it was found to record in the commit message? > Signed-off-by: Rob Clark <robdclark@chromium.org> Fixes: a4c1cdd34e2c ("drm/i915/gem: Delay context creation (v3)") References: 3aa9945a528e ("drm/i915: Separate GEM context construction and registration to userspace") Cc: <stable@vger.kernel.org> # v5.15+ > --- > drivers/gpu/drm/i915/gem/i915_gem_context.c | 24 +++++++++++++++------ > 1 file changed, 18 insertions(+), 6 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c > index 7f2831efc798..6250de9b9196 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c > @@ -1688,6 +1688,10 @@ void i915_gem_init__contexts(struct drm_i915_private *i915) > init_contexts(&i915->gem.contexts); > } > > +/* > + * Note that this implicitly consumes the ctx reference, by placing > + * the ctx in the context_xa. > + */ > static void gem_context_register(struct i915_gem_context *ctx, > struct drm_i915_file_private *fpriv, > u32 id) > @@ -1703,10 +1707,6 @@ static void gem_context_register(struct i915_gem_context *ctx, > snprintf(ctx->name, sizeof(ctx->name), "%s[%d]", > current->comm, pid_nr(ctx->pid)); > > - /* And finally expose ourselves to userspace via the idr */ > - old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); > - WARN_ON(old); > - > spin_lock(&ctx->client->ctx_lock); > list_add_tail_rcu(&ctx->client_link, &ctx->client->ctx_list); > spin_unlock(&ctx->client->ctx_lock); > @@ -1714,6 +1714,10 @@ static void gem_context_register(struct i915_gem_context *ctx, > spin_lock(&i915->gem.contexts.lock); > list_add_tail(&ctx->link, &i915->gem.contexts.list); > spin_unlock(&i915->gem.contexts.lock); > + > + /* And finally expose ourselves to userspace via the idr */ > + old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); > + WARN_ON(old); Have you seen that this hunk is needed or just moving it for a good measure? To be clear, it is probably best to move it even if the current placement cannot cause any problems, I am just double-checking if you had any concrete observations here while mulling over easier stable backports if we would omit it. > } > > int i915_gem_context_open(struct drm_i915_private *i915, > @@ -2199,14 +2203,22 @@ finalize_create_context_locked(struct drm_i915_file_private *file_priv, > if (IS_ERR(ctx)) > return ctx; > > + /* > + * One for the xarray and one for the caller. We need to grab > + * the reference *prior* to making the ctx visble to userspace > + * in gem_context_register(), as at any point after that > + * userspace can try to race us with another thread destroying > + * the context under our feet. > + */ > + i915_gem_context_get(ctx); > + > gem_context_register(ctx, file_priv, id); > > old = xa_erase(&file_priv->proto_context_xa, id); > GEM_BUG_ON(old != pc); > proto_context_close(file_priv->dev_priv, pc); > > - /* One for the xarray and one for the caller */ > - return i915_gem_context_get(ctx); > + return ctx; Otherwise userspace can look up a context which hasn't had it's reference count increased yep. I can add the Fixes: and Stable: tags while merging if no complaints. Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Regards, Tvrtko > } > > struct i915_gem_context *
On Wed, Jan 4, 2023 at 1:34 AM Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> wrote: > > > On 03/01/2023 23:49, Rob Clark wrote: > > From: Rob Clark <robdclark@chromium.org> > > > > gem_context_register() makes the context visible to userspace, and which > > point a separate thread can trigger the I915_GEM_CONTEXT_DESTROY ioctl. > > So we need to ensure that nothing uses the ctx ptr after this. And we > > need to ensure that adding the ctx to the xarray is the *last* thing > > that gem_context_register() does with the ctx pointer. > > Any backtraces from oopses or notes on how it was found to record in the commit message? It was a UAF bug that was reported to us https://bugs.chromium.org/p/chromium/issues/detail?id=1401594 (but I guess security bugs are not going to be visible) > > > Signed-off-by: Rob Clark <robdclark@chromium.org> > > Fixes: a4c1cdd34e2c ("drm/i915/gem: Delay context creation (v3)") > References: 3aa9945a528e ("drm/i915: Separate GEM context construction and registration to userspace") > Cc: <stable@vger.kernel.org> # v5.15+ > > > --- > > drivers/gpu/drm/i915/gem/i915_gem_context.c | 24 +++++++++++++++------ > > 1 file changed, 18 insertions(+), 6 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c > > index 7f2831efc798..6250de9b9196 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c > > @@ -1688,6 +1688,10 @@ void i915_gem_init__contexts(struct drm_i915_private *i915) > > init_contexts(&i915->gem.contexts); > > } > > > > +/* > > + * Note that this implicitly consumes the ctx reference, by placing > > + * the ctx in the context_xa. > > + */ > > static void gem_context_register(struct i915_gem_context *ctx, > > struct drm_i915_file_private *fpriv, > > u32 id) > > @@ -1703,10 +1707,6 @@ static void gem_context_register(struct i915_gem_context *ctx, > > snprintf(ctx->name, sizeof(ctx->name), "%s[%d]", > > current->comm, pid_nr(ctx->pid)); > > > > - /* And finally expose ourselves to userspace via the idr */ > > - old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); > > - WARN_ON(old); > > - > > spin_lock(&ctx->client->ctx_lock); > > list_add_tail_rcu(&ctx->client_link, &ctx->client->ctx_list); > > spin_unlock(&ctx->client->ctx_lock); > > @@ -1714,6 +1714,10 @@ static void gem_context_register(struct i915_gem_context *ctx, > > spin_lock(&i915->gem.contexts.lock); > > list_add_tail(&ctx->link, &i915->gem.contexts.list); > > spin_unlock(&i915->gem.contexts.lock); > > + > > + /* And finally expose ourselves to userspace via the idr */ > > + old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); > > + WARN_ON(old); > > Have you seen that this hunk is needed or just moving it for a good measure? To be clear, it is probably best to move it even if the current placement cannot cause any problems, I am just double-checking if you had any concrete observations here while mulling over easier stable backports if we would omit it. > This was actually the originally reported issue, the finalize_create_context_locked() part was something I found when the original report prompted me to audit gem_context_register() call paths. > > } > > > > int i915_gem_context_open(struct drm_i915_private *i915, > > @@ -2199,14 +2203,22 @@ finalize_create_context_locked(struct drm_i915_file_private *file_priv, > > if (IS_ERR(ctx)) > > return ctx; > > > > + /* > > + * One for the xarray and one for the caller. We need to grab > > + * the reference *prior* to making the ctx visble to userspace > > + * in gem_context_register(), as at any point after that > > + * userspace can try to race us with another thread destroying > > + * the context under our feet. > > + */ > > + i915_gem_context_get(ctx); > > + > > gem_context_register(ctx, file_priv, id); > > > > old = xa_erase(&file_priv->proto_context_xa, id); > > GEM_BUG_ON(old != pc); > > proto_context_close(file_priv->dev_priv, pc); > > > > - /* One for the xarray and one for the caller */ > > - return i915_gem_context_get(ctx); > > + return ctx; > > Otherwise userspace can look up a context which hasn't had it's reference count increased yep. I can add the Fixes: and Stable: tags while merging if no complaints. > > Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Thanks BR, -R > > Regards, > > Tvrtko > > > } > > > > struct i915_gem_context *
Hi Rob, On Tue, Jan 03, 2023 at 03:49:46PM -0800, Rob Clark wrote: > From: Rob Clark <robdclark@chromium.org> > > gem_context_register() makes the context visible to userspace, and which > point a separate thread can trigger the I915_GEM_CONTEXT_DESTROY ioctl. > So we need to ensure that nothing uses the ctx ptr after this. And we > need to ensure that adding the ctx to the xarray is the *last* thing > that gem_context_register() does with the ctx pointer. > > Signed-off-by: Rob Clark <robdclark@chromium.org> Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com> I also agree with Tvrtko that we should add Stable: and Fixes:. One little thing, "user after free" is clearer that UAF :) Thanks, Andi > --- > drivers/gpu/drm/i915/gem/i915_gem_context.c | 24 +++++++++++++++------ > 1 file changed, 18 insertions(+), 6 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c > index 7f2831efc798..6250de9b9196 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c > @@ -1688,6 +1688,10 @@ void i915_gem_init__contexts(struct drm_i915_private *i915) > init_contexts(&i915->gem.contexts); > } > > +/* > + * Note that this implicitly consumes the ctx reference, by placing > + * the ctx in the context_xa. > + */ > static void gem_context_register(struct i915_gem_context *ctx, > struct drm_i915_file_private *fpriv, > u32 id) > @@ -1703,10 +1707,6 @@ static void gem_context_register(struct i915_gem_context *ctx, > snprintf(ctx->name, sizeof(ctx->name), "%s[%d]", > current->comm, pid_nr(ctx->pid)); > > - /* And finally expose ourselves to userspace via the idr */ > - old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); > - WARN_ON(old); > - > spin_lock(&ctx->client->ctx_lock); > list_add_tail_rcu(&ctx->client_link, &ctx->client->ctx_list); > spin_unlock(&ctx->client->ctx_lock); > @@ -1714,6 +1714,10 @@ static void gem_context_register(struct i915_gem_context *ctx, > spin_lock(&i915->gem.contexts.lock); > list_add_tail(&ctx->link, &i915->gem.contexts.list); > spin_unlock(&i915->gem.contexts.lock); > + > + /* And finally expose ourselves to userspace via the idr */ > + old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); > + WARN_ON(old); > } > > int i915_gem_context_open(struct drm_i915_private *i915, > @@ -2199,14 +2203,22 @@ finalize_create_context_locked(struct drm_i915_file_private *file_priv, > if (IS_ERR(ctx)) > return ctx; > > + /* > + * One for the xarray and one for the caller. We need to grab > + * the reference *prior* to making the ctx visble to userspace > + * in gem_context_register(), as at any point after that > + * userspace can try to race us with another thread destroying > + * the context under our feet. > + */ > + i915_gem_context_get(ctx); > + > gem_context_register(ctx, file_priv, id); > > old = xa_erase(&file_priv->proto_context_xa, id); > GEM_BUG_ON(old != pc); > proto_context_close(file_priv->dev_priv, pc); > > - /* One for the xarray and one for the caller */ > - return i915_gem_context_get(ctx); > + return ctx; > } > > struct i915_gem_context * > -- > 2.38.1
On 05/01/2023 15:52, Andi Shyti wrote: > Hi Rob, > > On Tue, Jan 03, 2023 at 03:49:46PM -0800, Rob Clark wrote: >> From: Rob Clark <robdclark@chromium.org> >> >> gem_context_register() makes the context visible to userspace, and which >> point a separate thread can trigger the I915_GEM_CONTEXT_DESTROY ioctl. >> So we need to ensure that nothing uses the ctx ptr after this. And we >> need to ensure that adding the ctx to the xarray is the *last* thing >> that gem_context_register() does with the ctx pointer. >> >> Signed-off-by: Rob Clark <robdclark@chromium.org> > > Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com> > > I also agree with Tvrtko that we should add Stable: and Fixes:. Yeah I'll add them all when merging. Just waiting for full CI results. It will be like this: Fixes: eb4dedae920a ("drm/i915/gem: Delay tracking the GEM context until it is registered") Fixes: a4c1cdd34e2c ("drm/i915/gem: Delay context creation (v3)") Fixes: 49bd54b390c2 ("drm/i915: Track all user contexts per client") Cc: <stable@vger.kernel.org> # v5.10+ Regards, Tvrtko > One little thing, "user after free" is clearer that UAF :) > > Thanks, > Andi > >> --- >> drivers/gpu/drm/i915/gem/i915_gem_context.c | 24 +++++++++++++++------ >> 1 file changed, 18 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c >> index 7f2831efc798..6250de9b9196 100644 >> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c >> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c >> @@ -1688,6 +1688,10 @@ void i915_gem_init__contexts(struct drm_i915_private *i915) >> init_contexts(&i915->gem.contexts); >> } >> >> +/* >> + * Note that this implicitly consumes the ctx reference, by placing >> + * the ctx in the context_xa. >> + */ >> static void gem_context_register(struct i915_gem_context *ctx, >> struct drm_i915_file_private *fpriv, >> u32 id) >> @@ -1703,10 +1707,6 @@ static void gem_context_register(struct i915_gem_context *ctx, >> snprintf(ctx->name, sizeof(ctx->name), "%s[%d]", >> current->comm, pid_nr(ctx->pid)); >> >> - /* And finally expose ourselves to userspace via the idr */ >> - old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); >> - WARN_ON(old); >> - >> spin_lock(&ctx->client->ctx_lock); >> list_add_tail_rcu(&ctx->client_link, &ctx->client->ctx_list); >> spin_unlock(&ctx->client->ctx_lock); >> @@ -1714,6 +1714,10 @@ static void gem_context_register(struct i915_gem_context *ctx, >> spin_lock(&i915->gem.contexts.lock); >> list_add_tail(&ctx->link, &i915->gem.contexts.list); >> spin_unlock(&i915->gem.contexts.lock); >> + >> + /* And finally expose ourselves to userspace via the idr */ >> + old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); >> + WARN_ON(old); >> } >> >> int i915_gem_context_open(struct drm_i915_private *i915, >> @@ -2199,14 +2203,22 @@ finalize_create_context_locked(struct drm_i915_file_private *file_priv, >> if (IS_ERR(ctx)) >> return ctx; >> >> + /* >> + * One for the xarray and one for the caller. We need to grab >> + * the reference *prior* to making the ctx visble to userspace >> + * in gem_context_register(), as at any point after that >> + * userspace can try to race us with another thread destroying >> + * the context under our feet. >> + */ >> + i915_gem_context_get(ctx); >> + >> gem_context_register(ctx, file_priv, id); >> >> old = xa_erase(&file_priv->proto_context_xa, id); >> GEM_BUG_ON(old != pc); >> proto_context_close(file_priv->dev_priv, pc); >> >> - /* One for the xarray and one for the caller */ >> - return i915_gem_context_get(ctx); >> + return ctx; >> } >> >> struct i915_gem_context * >> -- >> 2.38.1
On 05/01/2023 16:00, Tvrtko Ursulin wrote: > > On 05/01/2023 15:52, Andi Shyti wrote: >> Hi Rob, >> >> On Tue, Jan 03, 2023 at 03:49:46PM -0800, Rob Clark wrote: >>> From: Rob Clark <robdclark@chromium.org> >>> >>> gem_context_register() makes the context visible to userspace, and which >>> point a separate thread can trigger the I915_GEM_CONTEXT_DESTROY ioctl. >>> So we need to ensure that nothing uses the ctx ptr after this. And we >>> need to ensure that adding the ctx to the xarray is the *last* thing >>> that gem_context_register() does with the ctx pointer. >>> >>> Signed-off-by: Rob Clark <robdclark@chromium.org> >> >> Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com> >> >> I also agree with Tvrtko that we should add Stable: and Fixes:. > > Yeah I'll add them all when merging. Just waiting for full CI results. > It will be like this: > > Fixes: eb4dedae920a ("drm/i915/gem: Delay tracking the GEM context until > it is registered") > Fixes: a4c1cdd34e2c ("drm/i915/gem: Delay context creation (v3)") > Fixes: 49bd54b390c2 ("drm/i915: Track all user contexts per client") > Cc: <stable@vger.kernel.org> # v5.10+ Pushed to drm-intel-gt-next - thanks for the fix and reviews. Regards, Tvrtko > > Regards, > > Tvrtko > >> One little thing, "user after free" is clearer that UAF :) >> >> Thanks, >> Andi >> >>> --- >>> drivers/gpu/drm/i915/gem/i915_gem_context.c | 24 +++++++++++++++------ >>> 1 file changed, 18 insertions(+), 6 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c >>> b/drivers/gpu/drm/i915/gem/i915_gem_context.c >>> index 7f2831efc798..6250de9b9196 100644 >>> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c >>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c >>> @@ -1688,6 +1688,10 @@ void i915_gem_init__contexts(struct >>> drm_i915_private *i915) >>> init_contexts(&i915->gem.contexts); >>> } >>> +/* >>> + * Note that this implicitly consumes the ctx reference, by placing >>> + * the ctx in the context_xa. >>> + */ >>> static void gem_context_register(struct i915_gem_context *ctx, >>> struct drm_i915_file_private *fpriv, >>> u32 id) >>> @@ -1703,10 +1707,6 @@ static void gem_context_register(struct >>> i915_gem_context *ctx, >>> snprintf(ctx->name, sizeof(ctx->name), "%s[%d]", >>> current->comm, pid_nr(ctx->pid)); >>> - /* And finally expose ourselves to userspace via the idr */ >>> - old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); >>> - WARN_ON(old); >>> - >>> spin_lock(&ctx->client->ctx_lock); >>> list_add_tail_rcu(&ctx->client_link, &ctx->client->ctx_list); >>> spin_unlock(&ctx->client->ctx_lock); >>> @@ -1714,6 +1714,10 @@ static void gem_context_register(struct >>> i915_gem_context *ctx, >>> spin_lock(&i915->gem.contexts.lock); >>> list_add_tail(&ctx->link, &i915->gem.contexts.list); >>> spin_unlock(&i915->gem.contexts.lock); >>> + >>> + /* And finally expose ourselves to userspace via the idr */ >>> + old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); >>> + WARN_ON(old); >>> } >>> int i915_gem_context_open(struct drm_i915_private *i915, >>> @@ -2199,14 +2203,22 @@ finalize_create_context_locked(struct >>> drm_i915_file_private *file_priv, >>> if (IS_ERR(ctx)) >>> return ctx; >>> + /* >>> + * One for the xarray and one for the caller. We need to grab >>> + * the reference *prior* to making the ctx visble to userspace >>> + * in gem_context_register(), as at any point after that >>> + * userspace can try to race us with another thread destroying >>> + * the context under our feet. >>> + */ >>> + i915_gem_context_get(ctx); >>> + >>> gem_context_register(ctx, file_priv, id); >>> old = xa_erase(&file_priv->proto_context_xa, id); >>> GEM_BUG_ON(old != pc); >>> proto_context_close(file_priv->dev_priv, pc); >>> - /* One for the xarray and one for the caller */ >>> - return i915_gem_context_get(ctx); >>> + return ctx; >>> } >>> struct i915_gem_context * >>> -- >>> 2.38.1
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c index 7f2831efc798..6250de9b9196 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -1688,6 +1688,10 @@ void i915_gem_init__contexts(struct drm_i915_private *i915) init_contexts(&i915->gem.contexts); } +/* + * Note that this implicitly consumes the ctx reference, by placing + * the ctx in the context_xa. + */ static void gem_context_register(struct i915_gem_context *ctx, struct drm_i915_file_private *fpriv, u32 id) @@ -1703,10 +1707,6 @@ static void gem_context_register(struct i915_gem_context *ctx, snprintf(ctx->name, sizeof(ctx->name), "%s[%d]", current->comm, pid_nr(ctx->pid)); - /* And finally expose ourselves to userspace via the idr */ - old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); - WARN_ON(old); - spin_lock(&ctx->client->ctx_lock); list_add_tail_rcu(&ctx->client_link, &ctx->client->ctx_list); spin_unlock(&ctx->client->ctx_lock); @@ -1714,6 +1714,10 @@ static void gem_context_register(struct i915_gem_context *ctx, spin_lock(&i915->gem.contexts.lock); list_add_tail(&ctx->link, &i915->gem.contexts.list); spin_unlock(&i915->gem.contexts.lock); + + /* And finally expose ourselves to userspace via the idr */ + old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); + WARN_ON(old); } int i915_gem_context_open(struct drm_i915_private *i915, @@ -2199,14 +2203,22 @@ finalize_create_context_locked(struct drm_i915_file_private *file_priv, if (IS_ERR(ctx)) return ctx; + /* + * One for the xarray and one for the caller. We need to grab + * the reference *prior* to making the ctx visble to userspace + * in gem_context_register(), as at any point after that + * userspace can try to race us with another thread destroying + * the context under our feet. + */ + i915_gem_context_get(ctx); + gem_context_register(ctx, file_priv, id); old = xa_erase(&file_priv->proto_context_xa, id); GEM_BUG_ON(old != pc); proto_context_close(file_priv->dev_priv, pc); - /* One for the xarray and one for the caller */ - return i915_gem_context_get(ctx); + return ctx; } struct i915_gem_context *