Check the edge case where batch_start_offset sits exactly on the batch
size.

v2: add new range_overflows variant to capture the special case where
the size is permitted to be zero, like with batch_len.

Testcase: igt/gem_exec_params/invalid-batch-start-offset
Fixes: 0b5372727be3 ("drm/i915/cmdparser: Use cached vmappings")
Signed-off-by: Matthew Auld <[email protected]>
Cc: Mika Kuoppala <[email protected]>
Cc: Chris Wilson <[email protected]>
---
 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c |  6 +++---
 drivers/gpu/drm/i915/i915_utils.h              | 12 ++++++++++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c 
b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 7bb27f382af7..43c05034ddb0 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -2714,9 +2714,9 @@ i915_gem_do_execbuffer(struct drm_device *dev,
                goto err_vma;
        }
 
-       if (range_overflows_t(u64,
-                             eb.batch_start_offset, eb.batch_len,
-                             eb.batch->vma->size)) {
+       if (range_overflows_end_t(u64,
+                                 eb.batch_start_offset, eb.batch_len,
+                                 eb.batch->vma->size)) {
                drm_dbg(&i915->drm, "Attempting to use out-of-bounds batch\n");
                err = -EINVAL;
                goto err_vma;
diff --git a/drivers/gpu/drm/i915/i915_utils.h 
b/drivers/gpu/drm/i915/i915_utils.h
index cae0ae520398..4cb74564e2dd 100644
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -108,6 +108,18 @@ bool i915_error_injected(void);
 #define range_overflows_t(type, start, size, max) \
        range_overflows((type)(start), (type)(size), (type)(max))
 
+#define range_overflows_end(start, size, max) ({ \
+       typeof(start) start__ = (start); \
+       typeof(size) size__ = (size); \
+       typeof(max) max__ = (max); \
+       (void)(&start__ == &size__); \
+       (void)(&start__ == &max__); \
+       start__ >= max__ || size__ > max__ - start__; \
+})
+
+#define range_overflows_end_t(type, start, size, max) \
+       range_overflows_end((type)(start), (type)(size), (type)(max))
+
 /* Note we don't consider signbits :| */
 #define overflows_type(x, T) \
        (sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T))
-- 
2.20.1

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