[Intel-gfx] [PATCH v9 1/8] overflow: Move and add few utility macros into overflow
Gwan-gyeong Mun
gwan-gyeong.mun at intel.com
Fri Sep 9 10:52:41 UTC 2022
On 8/26/22 10:44 PM, Andrzej Hajda wrote:
> On 25.08.2022 18:47, Kees Cook wrote:
>> 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 at intel.com>
>>> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>>> Cc: Matthew Auld <matthew.auld at intel.com>
>>> Cc: Nirmoy Das <nirmoy.das at intel.com>
>>> Cc: Jani Nikula <jani.nikula at intel.com>
>>> Cc: Andi Shyti <andi.shyti at linux.intel.com>
>>> Cc: Andrzej Hajda <andrzej.hajda at intel.com>
>>> Cc: Mauro Carvalho Chehab <mauro.chehab at linux.intel.com>
>>> Cc: Kees Cook <keescook at chromium.org>
>>> Reviewed-by: Mauro Carvalho Chehab <mchehab at kernel.org> (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. :)
>
>
> One more thing, I suspect __builtin_add_overflow checks already if ptr
> is pointer, so typecheck_pointer seems redundant.
>
thanks for check in detail.
I'll remove redundant code and send new version.
> Regards
> Andrzej
>
>
>>
>>> +
>>> /*
>>> * For simplicity and code hygiene, the fallback code below insists on
>>> * a, b and *d having the same type (similar to the min() and max()
>>> --
>>> 2.37.1
>>>
>>
>> -Kees
>>
>> [1] 4eb6bd55cfb2 ("compiler.h: drop fallback overflow checkers")
>>
>
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