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 +++++
.../drm/i915/gem/selftests/i915_gem_mman.c | 120 ++++++++++++++++++
2 files changed, 151 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,
};
diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
index ef7abcb3f4ee..903022ee6083 100644
--- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
@@ -952,6 +952,125 @@ static int igt_mmap(void *arg)
return 0;
}
+static const char *repr_mmap_type(enum i915_mmap_type type)
+{
+ switch (type) {
+ case I915_MMAP_TYPE_GTT: return "gtt";
+ case I915_MMAP_TYPE_WB: return "wb";
+ case I915_MMAP_TYPE_WC: return "wc";
+ case I915_MMAP_TYPE_UC: return "uc";
+ default: return "unknown";
+ }
+}
+
+static bool can_access(const struct drm_i915_gem_object *obj)
+{
+ unsigned int flags =
+ I915_GEM_OBJECT_HAS_STRUCT_PAGE | I915_GEM_OBJECT_HAS_IOMEM;
+
+ return i915_gem_object_type_has(obj, flags);
+}
+
+static int __igt_mmap_access(struct drm_i915_private *i915,
+ struct drm_i915_gem_object *obj,
+ enum i915_mmap_type type)
+{
+ struct i915_mmap_offset *mmo;
+ unsigned long __user *ptr;
+ unsigned long A, B;
+ unsigned long x, y;
+ u64 addr;
+ int err;
+
+ memset(&A, 0xAA, sizeof(A));
+ memset(&B, 0xBB, sizeof(B));
+
+ if (!can_mmap(obj, type) || !can_access(obj))
+ return 0;
+
+ mmo = mmap_offset_attach(obj, type, NULL);
+ if (IS_ERR(mmo))
+ return PTR_ERR(mmo);
+
+ addr = igt_mmap_node(i915, &mmo->vma_node, 0, PROT_WRITE, MAP_SHARED);
+ if (IS_ERR_VALUE(addr))
+ return addr;
+ ptr = u64_to_user_ptr(addr);
+
+ err = __put_user(A, ptr);
+ if (err) {
+ pr_err("%s(%s): failed to write into user mmap\n",
+ obj->mm.region->name, repr_mmap_type(type));
+ goto out_unmap;
+ }
+
+ err = access_process_vm(current, addr, &x, sizeof(x), 0);
+ if (err != sizeof(x)) {
+ pr_err("%s(%s): access_process_vm() read failed\n",
+ obj->mm.region->name, repr_mmap_type(type));
+ goto out_unmap;
+ }
+
+ err = access_process_vm(current, addr, &B, sizeof(B), FOLL_WRITE);
+ if (err != sizeof(B)) {
+ pr_err("%s(%s): access_process_vm() write failed\n",
+ obj->mm.region->name, repr_mmap_type(type));
+ goto out_unmap;
+ }
+
+ err = __get_user(y, ptr);
+ if (err) {
+ pr_err("%s(%s): failed to read from user mmap\n",
+ obj->mm.region->name, repr_mmap_type(type));
+ goto out_unmap;
+ }
+
+ if (x != A || y != B) {
+ pr_err("%s(%s): failed to read/write values, found (%lx, %lx)\n",
+ obj->mm.region->name, repr_mmap_type(type),
+ x, y);
+ err = -EINVAL;
+ goto out_unmap;
+ }
+
+out_unmap:
+ vm_munmap(addr, obj->base.size);
+ return err;
+}
+
+static int igt_mmap_access(void *arg)
+{
+ struct drm_i915_private *i915 = arg;
+ struct intel_memory_region *mr;
+ enum intel_region_id id;
+
+ for_each_memory_region(mr, i915, id) {
+ struct drm_i915_gem_object *obj;
+ int err;
+
+ obj = i915_gem_object_create_region(mr, PAGE_SIZE, 0);
+ if (obj == ERR_PTR(-ENODEV))
+ continue;
+
+ if (IS_ERR(obj))
+ return PTR_ERR(obj);
+
+ err = __igt_mmap_access(i915, obj, I915_MMAP_TYPE_GTT);
+ if (err == 0)
+ err = __igt_mmap_access(i915, obj, I915_MMAP_TYPE_WB);
+ if (err == 0)
+ err = __igt_mmap_access(i915, obj, I915_MMAP_TYPE_WC);
+ if (err == 0)
+ err = __igt_mmap_access(i915, obj, I915_MMAP_TYPE_UC);
+
+ i915_gem_object_put(obj);
+ if (err)
+ return err;
+ }
+
+ return 0;
+}
+
static int __igt_mmap_gpu(struct drm_i915_private *i915,
struct drm_i915_gem_object *obj,
enum i915_mmap_type type)
@@ -1229,6 +1348,7 @@ int i915_gem_mman_live_selftests(struct drm_i915_private *i915)
SUBTEST(igt_smoke_tiling),
SUBTEST(igt_mmap_offset_exhaustion),
SUBTEST(igt_mmap),
+ SUBTEST(igt_mmap_access),
SUBTEST(igt_mmap_revoke),
SUBTEST(igt_mmap_gpu),
};
--
2.20.1
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