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drm/i915: Fix potential context UAFs

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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>
Fixes: eb4dedae92 ("drm/i915/gem: Delay tracking the GEM context until it is registered")
Fixes: a4c1cdd34e ("drm/i915/gem: Delay context creation (v3)")
Fixes: 49bd54b390 ("drm/i915: Track all user contexts per client")
Cc: <stable@vger.kernel.org> # v5.10+
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
[tursulin: Stable and fixes tags add/tidy.]
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230103234948.1218393-1-robdclark@gmail.com
(cherry picked from commit bed4b455cf)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
This commit is contained in:
Rob Clark
2023-01-03 15:49:46 -08:00
committed by Rodrigo Vivi
parent 476fdcdaaa
commit afce71ff6d
1 changed files with 18 additions and 6 deletions
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24
drivers/gpu/drm/i915/gem/i915_gem_context.c
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@@ -1688,6 +1688,10 @@ void i915_gem_init__contexts(struct drm_i915_private *i915)
init_contexts(&i915->gem.contexts); 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, static void gem_context_register(struct i915_gem_context *ctx,
struct drm_i915_file_private *fpriv, struct drm_i915_file_private *fpriv,
u32 id) u32 id)
@@ -1703,10 +1707,6 @@ static void gem_context_register(struct i915_gem_context *ctx,
snprintf(ctx->name, sizeof(ctx->name), "%s[%d]", snprintf(ctx->name, sizeof(ctx->name), "%s[%d]",
current->comm, pid_nr(ctx->pid)); 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); spin_lock(&ctx->client->ctx_lock);
list_add_tail_rcu(&ctx->client_link, &ctx->client->ctx_list); list_add_tail_rcu(&ctx->client_link, &ctx->client->ctx_list);
spin_unlock(&ctx->client->ctx_lock); 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); spin_lock(&i915->gem.contexts.lock);
list_add_tail(&ctx->link, &i915->gem.contexts.list); list_add_tail(&ctx->link, &i915->gem.contexts.list);
spin_unlock(&i915->gem.contexts.lock); 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, 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)) if (IS_ERR(ctx))
return 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); gem_context_register(ctx, file_priv, id);
old = xa_erase(&file_priv->proto_context_xa, id); old = xa_erase(&file_priv->proto_context_xa, id);
GEM_BUG_ON(old != pc); GEM_BUG_ON(old != pc);
proto_context_close(file_priv->dev_priv, pc); proto_context_close(file_priv->dev_priv, pc);
/* One for the xarray and one for the caller */ return ctx;
return i915_gem_context_get(ctx);
} }
struct i915_gem_context * struct i915_gem_context *