Messages in this thread | | | Date | Fri, 26 Aug 2022 15:44:36 +0200 | Subject | Re: [Intel-gfx] [PATCH v9 1/8] overflow: Move and add few utility macros into overflow | From | Andrzej Hajda <> |
| |
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@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 | 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.
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") >
| |