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arm64: Use pointer masking to limit uaccess speculation

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Similarly to x86, mitigate speculation past an access_ok() check by
masking the pointer against the address limit before use.

Even if we don't expect speculative writes per se, it is plausible that
a CPU may still speculate at least as far as fetching a cache line for
writing, hence we also harden put_user() and clear_user() for peace of
mind.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Robin Murphy 2018-02-05 15:34:19 +00:00 committed by Catalin Marinas
parent 51369e398d
commit 4d8efc2d5e
1 changed files with 23 additions and 3 deletions
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26
arch/arm64/include/asm/uaccess.h
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@ -227,6 +227,26 @@ static inline void uaccess_enable_not_uao(void)
__uaccess_enable(ARM64_ALT_PAN_NOT_UAO);
}
/*
* Sanitise a uaccess pointer such that it becomes NULL if above the
* current addr_limit.
*/
#define uaccess_mask_ptr(ptr) (__typeof__(ptr))__uaccess_mask_ptr(ptr)
static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
{
void __user *safe_ptr;
asm volatile(
" bics xzr, %1, %2\n"
" csel %0, %1, xzr, eq\n"
: "=&r" (safe_ptr)
: "r" (ptr), "r" (current_thread_info()->addr_limit)
: "cc");
csdb();
return safe_ptr;
}
/*
* The "__xxx" versions of the user access functions do not verify the address
* space - it must have been done previously with a separate "access_ok()"
@ -297,7 +317,7 @@ do { \
__typeof__(*(ptr)) __user *__p = (ptr); \
might_fault(); \
access_ok(VERIFY_READ, __p, sizeof(*__p)) ? \
__get_user((x), __p) : \
__p = uaccess_mask_ptr(__p), __get_user((x), __p) : \
((x) = 0, -EFAULT); \
})
@ -361,7 +381,7 @@ do { \
__typeof__(*(ptr)) __user *__p = (ptr); \
might_fault(); \
access_ok(VERIFY_WRITE, __p, sizeof(*__p)) ? \
__put_user((x), __p) : \
__p = uaccess_mask_ptr(__p), __put_user((x), __p) : \
-EFAULT; \
})
@ -377,7 +397,7 @@ extern unsigned long __must_check __clear_user(void __user *addr, unsigned long
static inline unsigned long __must_check clear_user(void __user *to, unsigned long n)
{
if (access_ok(VERIFY_WRITE, to, n))
n = __clear_user(to, n);
n = __clear_user(__uaccess_mask_ptr(to), n);
return n;
}