gdb uses ptrace() to peek and poke bytes of the target's address space.
The driver must implement an vm_ops->access() handler or else gdb will
be unable to inspect the pointer and report it as out-of-bounds.
Worse than useless as it causes immediate suspicion of the valid GTT
pointer, distracting the poor programmer trying to find his bug.
Testcase: igt/gem_mmap_gtt/ptrace
Testcase: igt/gem_mmap_offset/ptrace
Suggested-by: Kristian H. Kristensen <hoegsberg@xxxxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Maciej Patelczyk <maciej.patelczyk@xxxxxxxxx>
Cc: Kristian H. Kristensen <hoegsberg@xxxxxxxxxx>
---
drivers/gpu/drm/i915/gem/i915_gem_mman.c | 31 ++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
index b39c24dae64e..aef917b7f168 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
@@ -396,6 +396,35 @@ static vm_fault_t vm_fault_gtt(struct vm_fault *vmf)
return i915_error_to_vmf_fault(ret);
}
+static int
+vm_access(struct vm_area_struct *area, unsigned long addr,
+ void *buf, int len, int write)
+{
+ struct i915_mmap_offset *mmo = area->vm_private_data;
+ struct drm_i915_gem_object *obj = mmo->obj;
+ void *vaddr;
+
+ addr -= area->vm_start;
+ if (addr >= obj->base.size)
+ return -EINVAL;
+
+ /* As this is primarily for debugging, let's focus on simplicity */
+ vaddr = i915_gem_object_pin_map(obj, I915_MAP_FORCE_WC);
+ if (IS_ERR(vaddr))
+ return PTR_ERR(vaddr);
+
+ if (write) {
+ memcpy(vaddr + addr, buf, len);
+ __i915_gem_object_flush_map(obj, addr, len);
+ } else {
+ memcpy(buf, vaddr + addr, len);
+ }
+
+ i915_gem_object_unpin_map(obj);
+
+ return len;
+}
+
void __i915_gem_object_release_mmap_gtt(struct drm_i915_gem_object *obj)
{
struct i915_vma *vma;
@@ -745,12 +774,14 @@ static void vm_close(struct vm_area_struct *vma)
static const struct vm_operations_struct vm_ops_gtt = {
.fault = vm_fault_gtt,
+ .access = vm_access,
.open = vm_open,
.close = vm_close,
};
static const struct vm_operations_struct vm_ops_cpu = {
.fault = vm_fault_cpu,
+ .access = vm_access,
.open = vm_open,
.close = vm_close,
};
--
2.20.1
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