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Message-ID: <89531bbc-03f3-6212-d2c8-939a0e3261ab@intel.com>
Date: Wed, 24 Aug 2022 18:31:15 +0900
From: Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>
To: Andrzej Hajda <andrzej.hajda@...el.com>,
<intel-gfx@...ts.freedesktop.org>
CC: <thomas.hellstrom@...ux.intel.com>, <keescook@...omium.org>,
<jani.nikula@...el.com>, <linux-kernel@...r.kernel.org>,
<dri-devel@...ts.freedesktop.org>, <chris@...is-wilson.co.uk>,
<airlied@...ux.ie>, <matthew.auld@...el.com>, <daniel@...ll.ch>,
<intel-gfx-trybot@...ts.freedesktop.org>, <mchehab@...nel.org>,
<nirmoy.das@...el.com>
Subject: Re: [Intel-gfx] [PATCH v8 1/8] overflow: Move and add few utility
macros into overflow
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@...el.com>
>> Cc: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
>> Cc: Matthew Auld <matthew.auld@...el.com>
>> Cc: Nirmoy Das <nirmoy.das@...el.com>
>> Cc: Jani Nikula <jani.nikula@...el.com>
>> Cc: Andi Shyti <andi.shyti@...ux.intel.com>
>> Cc: Andrzej Hajda <andrzej.hajda@...el.com>
>> Cc: Mauro Carvalho Chehab <mauro.chehab@...ux.intel.com>
>> Cc: Kees Cook <keescook@...omium.org>
>> Reviewed-by: Mauro Carvalho Chehab <mchehab@...nel.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()
>
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