On Wed, Aug 24, 2022 at 05:45:07PM +0900, Gwan-gyeong Mun wrote:
It moves overflows_type utility macro into overflow header from i915_utils
header. The overflows_type can be used to catch the truncaion (overflow)
between different data types. And it adds check_assign() macro which
performs an assigning source value into destination ptr along with an
overflow check. overflow_type macro has been improved to handle the signbit
by gcc's built-in overflow check function. And it adds overflows_ptr()
helper macro for checking the overflows between a value and a pointer
type/value.
v3: Add is_type_unsigned() macro (Mauro)
Modify overflows_type() macro to consider signed data types (Mauro)
Fix the problem that safe_conversion() macro always returns true
v4: Fix kernel-doc markups
v6: Move macro addition location so that it can be used by other than drm
subsystem (Jani, Mauro, Andi)
Change is_type_unsigned to is_unsigned_type to have the same name form
as is_signed_type macro
v8: Add check_assign() and remove safe_conversion() (Kees)
Fix overflows_type() to use gcc's built-in overflow function (Andrzej)
Add overflows_ptr() to allow overflow checking when assigning a value
into a pointer variable (G.G.)
v9: Fix overflows_type() to use __builtin_add_overflow() instead of
__builtin_add_overflow_p() (Andrzej)
Fix overflows_ptr() to use overflows_type() with the unsigned long type
(Andrzej)
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Nirmoy Das <nirmoy.das@xxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
Cc: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
Cc: Mauro Carvalho Chehab <mauro.chehab@xxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> (v5)
---
drivers/gpu/drm/i915/i915_user_extensions.c | 3 +-
drivers/gpu/drm/i915/i915_utils.h | 5 +-
include/linux/overflow.h | 62 +++++++++++++++++++++
3 files changed, 64 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_user_extensions.c b/drivers/gpu/drm/i915/i915_user_extensions.c
index c822d0aafd2d..6f6b5b910968 100644
--- a/drivers/gpu/drm/i915/i915_user_extensions.c
+++ b/drivers/gpu/drm/i915/i915_user_extensions.c
@@ -50,8 +50,7 @@ int i915_user_extensions(struct i915_user_extension __user *ext,
if (err)
return err;
- if (get_user(next, &ext->next_extension) ||
- overflows_type(next, ext))
+ if (get_user(next, &ext->next_extension) || overflows_ptr(next))
return -EFAULT;
ext = u64_to_user_ptr(next);
I continue to dislike the layers of macros and specialization here.
This is just a fancy version of check_assign():
if (get_user(next, &ext->next_extension) || check_assign(next, &ext))
return -EFAULT;
However, the __builtin_*_overflow() family only wants to work on
integral types, so this needs to be slightly expanded:
uintptr_t kptr;
...
if (get_user(next, &ext->next_extension) || check_assign(next, &kptr))
return -EFAULT;
ext = (void * __user)kptr;
But, it does seem like the actual problem here is that u64_to_user_ptr()
is not performing the checking? It's used heavily in the drm code.
Is a check_assign_user_ptr() needed?
diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
index c10d68cdc3ca..eb0ded23fa9c 100644
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -32,6 +32,7 @@
#include <linux/types.h>
#include <linux/workqueue.h>
#include <linux/sched/clock.h>
+#include <linux/overflow.h>
#ifdef CONFIG_X86
#include <asm/hypervisor.h>
@@ -111,10 +112,6 @@ bool i915_error_injected(void);
#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))
-
#define ptr_mask_bits(ptr, n) ({ \
unsigned long __v = (unsigned long)(ptr); \
(typeof(ptr))(__v & -BIT(n)); \
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index f1221d11f8e5..6af9df1d67a1 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -52,6 +52,68 @@ static inline bool __must_check __must_check_overflow(bool overflow)
return unlikely(overflow);
}
+/**
+ * overflows_type - helper for checking the overflows between data types or
+ * values
+ *
+ * @x: Source value or data type for overflow check
+ * @T: Destination value or data type for overflow check
+ *
+ * It compares the values or data type between the first and second argument to
+ * check whether overflow can occur when assigning the first argument to the
+ * variable of the second argument. Source and Destination can be singned or
+ * unsigned data types. Source and Destination can be different data types.
+ *
+ * Returns:
+ * True if overflow can occur, false otherwise.
+ */
+#define overflows_type(x, T) __must_check_overflow(({ \
+ typeof(T) v = 0; \
+ __builtin_add_overflow((x), v, &v); \
+}))
I'd like to avoid "externalizing" these kinds of checks when the better
path is to catch the issue at operation type (add, sub, mul, assign).
Looking at existing users, I see stuff like:
if (overflows_type(item.query_id - 1, unsigned long))
return -EINVAL;
func_idx = item.query_id - 1;
This requires too much open-coded checking, IMO. It's better as:
if (check_assign(item.query_id - 1, &func_idx))
return -EINVAL;
or other similar:
if (overflows_type(user->slice_mask, context->slice_mask) ||
...
context->slice_mask = user->slice_mask;
and some that don't make sense to me. Why check argument types? Is this
trying to avoid implicit type conversions?
So, if it's _really_ needed, I can live with adding overflows_type().
+
+/**
+ * overflows_ptr - helper for checking the occurrence of overflows when a value
+ * assigns to the pointer data type
+ *
+ * @x: Source value for overflow check
+ *
+ * gcc's built-in overflow check functions don't support checking between the
+ * pointer type and non-pointer type. And ILP32 and LP64 have the same bit size
+ * between long and pointer. Therefore it internally compares the source value
+ * and unsigned long data type for checking overflow.
+ *
+ * Returns:
+ * True if overflow can occur, false otherwise.
+ */
+#define overflows_ptr(x) __must_check_overflow(overflows_type(x, unsigned long))
I'd rather not have this -- it's just a specialized use of
overflows_type(), and only used in 1 place.
+
+/**
+ * check_assign - perform an assigning source value into destination ptr along
+ * with an overflow check.
+ *
+ * @value: Source value
+ * @ptr: Destination pointer address, If the pointer type is not used,
+ * a warning message is output during build.
+ *
+ * It checks internally the ptr is a pointer type. And it uses gcc's built-in
+ * overflow check function.
+ * It does not use the check_*() wrapper functions, but directly uses gcc's
+ * built-in overflow check function so that it can be used even when
+ * the type of value and the type pointed to by ptr are different without build
+ * warning messages.
This is a good point: the check_{add,sub,mul}_overflow() helpers
currently require all the params be the same type, which rather limits
their usage. Perhaps this can be weakened now that we're not using[1]
the fallback logic any more? (Separate patch.)
+ *
+ * Returns:
+ * If the value would overflow the destination, it returns true. If not return
+ * false. When overflow does not occur, the assigning into ptr from value
+ * succeeds. It follows the return policy as other check_*_overflow() functions
+ * return non-zero as a failure.
+ */
+#define check_assign(value, ptr) __must_check_overflow(({ \
+ typecheck_pointer(ptr); \
+ __builtin_add_overflow(0, value, ptr); \
+}))
But yes, this looks correct. I really like it. :)
