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Date:   Wed, 24 Aug 2022 18:31:15 +0900
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Subject: Re: [Intel-gfx] [PATCH v8 1/8] overflow: Move and add few utility
 macros into overflow
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To:     Andrzej Hajda <andrzej.hajda@intel.com>,
        <intel-gfx@lists.freedesktop.org>
CC:     <thomas.hellstrom@linux.intel.com>, <keescook@chromium.org>,
        <jani.nikula@intel.com>, <linux-kernel@vger.kernel.org>,
        <dri-devel@lists.freedesktop.org>, <chris@chris-wilson.co.uk>,
        <airlied@linux.ie>, <matthew.auld@intel.com>, <daniel@ffwll.ch>,
        <intel-gfx-trybot@lists.freedesktop.org>, <mchehab@kernel.org>,
        <nirmoy.das@intel.com>
References: <20220823101729.2098841-1-gwan-gyeong.mun@intel.com>
 <20220823101729.2098841-2-gwan-gyeong.mun@intel.com>
 <44d2da7f-6632-8382-73c9-6df76b7eae0c@intel.com>
From:   Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
In-Reply-To: <44d2da7f-6632-8382-73c9-6df76b7eae0c@intel.com>
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On 8/23/22 9:35 PM, Andrzej Hajda wrote:
> On 23.08.2022 12:17, 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.)
>>
>> Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
>> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>> Cc: Matthew Auld <matthew.auld@intel.com>
>> Cc: Nirmoy Das <nirmoy.das@intel.com>
>> Cc: Jani Nikula <jani.nikula@intel.com>
>> Cc: Andi Shyti <andi.shyti@linux.intel.com>
>> Cc: Andrzej Hajda <andrzej.hajda@intel.com>
>> Cc: Mauro Carvalho Chehab <mauro.chehab@linux.intel.com>
>> Cc: Kees Cook <keescook@chromium.org>
>> Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org> (v5)
>> ---
>>   drivers/gpu/drm/i915/i915_user_extensions.c |  2 +-
>>   drivers/gpu/drm/i915/i915_utils.h           |  5 +-
>>   include/linux/overflow.h                    | 67 +++++++++++++++++++++
>>   3 files changed, 69 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_user_extensions.c 
>> b/drivers/gpu/drm/i915/i915_user_extensions.c
>> index c822d0aafd2d..0fb2fecbcaae 100644
>> --- a/drivers/gpu/drm/i915/i915_user_extensions.c
>> +++ b/drivers/gpu/drm/i915/i915_user_extensions.c
>> @@ -51,7 +51,7 @@ int i915_user_extensions(struct i915_user_extension 
>> __user *ext,
>>               return err;
>>           if (get_user(next, &ext->next_extension) ||
>> -            overflows_type(next, ext))
>> +            overflows_ptr(next, ext))
>>               return -EFAULT;
>>           ext = u64_to_user_ptr(next);
>> 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..4016f1378bcc 100644
>> --- a/include/linux/overflow.h
>> +++ b/include/linux/overflow.h
>> @@ -52,6 +52,73 @@ 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.
>> + *
>> + * Returns:
>> + * True if overflow can occur, false otherwise.
>> + */
>> +#define overflows_type(x, T) __must_check_overflow(({    \
>> +    typeof(T) v = 0;                \
>> +    __builtin_add_overflow_p((x), v, v);        \
> 
> 
> Above works since gcc7, since gcc5 you can use:
>      __builtin_add_overflow((x), v, &v);
> 
Yes I'll update it to use __builtin_add_overflow() like where the gcc's 
overflow check built-in function was used.
> 
>> +}))
>> +
>> +/**
>> + * overflows_ptr - helper for checking the overflows between a value and
>> + *                 a pointer type/value
>> + *
>> + * @x: Source value for overflow check
>> + * @T: Destination pointer type or value for overflow check
>> + *
>> + * gcc's built-in overflow check functions don't support checking 
>> between the
>> + * pointer type and non-pointer type. Therefore it compares the 
>> values and
>> + * size of each data type between the first and second argument to 
>> check whether
>> + * truncation can occur when assigning the first argument to the 
>> variable of the
>> + * second argument. It checks internally the ptr is a pointer type.
>> + *
>> + * Returns:
>> + * True if overflow can occur, false otherwise.
>> + */
>> +#define overflows_ptr(x, T) __must_check_overflow(({    \
>> +    typecheck_pointer(T);                \
>> +    ((x) < 0) ? 1 : (sizeof(x) > sizeof(T) && (x) >> 
>> BITS_PER_TYPE(T)) ? 1 : 0; \
>> +}))
> 
> 
> Doesn't linux assume that all pointers have size of long int ?
> Or at least all pointers have the same size.
> In such case we can use:
> #define overflows_ptr(x) overflows_type(x, unsigned long)
> 
yes it looks a better way. I'll update the macro and comments.

Thanks Andrzej

G.G.
> Regards
> Andrzej
> 
>> +
>> +/**
>> + * 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.
>> + *
>> + * 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);    \
>> +}))
>> +
>>   /*
>>    * 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()
>