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author | Chris Wilson <chris@chris-wilson.co.uk> | 2019-04-01 14:39:09 +0100 |
---|---|---|
committer | Chris Wilson <chris@chris-wilson.co.uk> | 2019-04-02 14:28:10 +0100 |
commit | b01720bfcdf9d4410a2968fac0769246ea3de81b (patch) | |
tree | c8d653bfbd9995f6c5a85f96a1c84069f6427f12 | |
parent | d53fef0be4a5f2f12219c231cdb6f838fbbf680c (diff) | |
download | linux-stable-b01720bfcdf9d4410a2968fac0769246ea3de81b.tar.gz linux-stable-b01720bfcdf9d4410a2968fac0769246ea3de81b.tar.bz2 linux-stable-b01720bfcdf9d4410a2968fac0769246ea3de81b.zip |
drm/i915: Prefault before locking pages in shmem_pwrite
If the user passes in a pointer to a GGTT mmaping of the same buffer
being written to, we can hit a deadlock in acquiring the shmemfs page
(once as the write destination and then as the read source).
[<0>] io_schedule+0xd/0x30
[<0>] __lock_page+0x105/0x1b0
[<0>] find_lock_entry+0x55/0x90
[<0>] shmem_getpage_gfp+0xbb/0x800
[<0>] shmem_read_mapping_page_gfp+0x2d/0x50
[<0>] shmem_get_pages+0x158/0x5d0 [i915]
[<0>] ____i915_gem_object_get_pages+0x17/0x90 [i915]
[<0>] __i915_gem_object_get_pages+0x57/0x70 [i915]
[<0>] i915_gem_fault+0x1b4/0x5c0 [i915]
[<0>] __do_fault+0x2d/0x80
[<0>] __handle_mm_fault+0xad4/0xfb0
[<0>] handle_mm_fault+0xe6/0x1f0
[<0>] __do_page_fault+0x18f/0x3f0
[<0>] page_fault+0x1b/0x20
[<0>] copy_user_enhanced_fast_string+0x7/0x10
[<0>] _copy_from_user+0x37/0x60
[<0>] shmem_pwrite+0xf0/0x160 [i915]
[<0>] i915_gem_pwrite_ioctl+0x14e/0x520 [i915]
[<0>] drm_ioctl_kernel+0x81/0xd0
[<0>] drm_ioctl+0x1a7/0x310
[<0>] do_vfs_ioctl+0x88/0x5d0
[<0>] ksys_ioctl+0x35/0x70
[<0>] __x64_sys_ioctl+0x11/0x20
[<0>] do_syscall_64+0x39/0xe0
[<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
We can reduce (but not eliminate!) the chance of this happening by
faulting the user_data before we take the page lock in
pagecache_write_begin(). One way to eliminate the potential recursion
here is by disabling pagefaults for the copy, and handling the fallback
to use an alternative method -- so convert to use kmap_atomic (which
should disable preemption and pagefaulting for the copy) and report
ENODEV instead of EFAULT so that our caller tries again with a different
copy mechanism -- we already check that the page should have been
faultable so a false negative should be rare.
Testcase: igt/gem_pwrite/self
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Reviewed-by: Matthew Auld <matthew.william.auld@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190401133909.31203-1-chris@chris-wilson.co.uk
-rw-r--r-- | drivers/gpu/drm/i915/i915_gem.c | 30 |
1 files changed, 24 insertions, 6 deletions
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index c3b4ec52e1b7..bf594a5e88bc 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2788,7 +2788,11 @@ i915_gem_object_pwrite_gtt(struct drm_i915_gem_object *obj, u64 remain, offset; unsigned int pg; - /* Before we instantiate/pin the backing store for our use, we + /* Caller already validated user args */ + GEM_BUG_ON(!access_ok(user_data, arg->size)); + + /* + * Before we instantiate/pin the backing store for our use, we * can prepopulate the shmemfs filp efficiently using a write into * the pagecache. We avoid the penalty of instantiating all the * pages, important if the user is just writing to a few and never @@ -2802,7 +2806,8 @@ i915_gem_object_pwrite_gtt(struct drm_i915_gem_object *obj, if (obj->mm.madv != I915_MADV_WILLNEED) return -EFAULT; - /* Before the pages are instantiated the object is treated as being + /* + * Before the pages are instantiated the object is treated as being * in the CPU domain. The pages will be clflushed as required before * use, and we can freely write into the pages directly. If userspace * races pwrite with any other operation; corruption will ensue - @@ -2818,20 +2823,32 @@ i915_gem_object_pwrite_gtt(struct drm_i915_gem_object *obj, struct page *page; void *data, *vaddr; int err; + char c; len = PAGE_SIZE - pg; if (len > remain) len = remain; + /* Prefault the user page to reduce potential recursion */ + err = __get_user(c, user_data); + if (err) + return err; + + err = __get_user(c, user_data + len - 1); + if (err) + return err; + err = pagecache_write_begin(obj->base.filp, mapping, offset, len, 0, &page, &data); if (err < 0) return err; - vaddr = kmap(page); - unwritten = copy_from_user(vaddr + pg, user_data, len); - kunmap(page); + vaddr = kmap_atomic(page); + unwritten = __copy_from_user_inatomic(vaddr + pg, + user_data, + len); + kunmap_atomic(vaddr); err = pagecache_write_end(obj->base.filp, mapping, offset, len, len - unwritten, @@ -2839,8 +2856,9 @@ i915_gem_object_pwrite_gtt(struct drm_i915_gem_object *obj, if (err < 0) return err; + /* We don't handle -EFAULT, leave it to the caller to check */ if (unwritten) - return -EFAULT; + return -ENODEV; remain -= len; user_data += len; |