This is a note to let you know that I've just added the patch titled
[Variant 1/Spectre-v1] arm64: Use pointer masking to limit uaccess speculation
to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-use-pointer-masking-to-limit-uaccess-speculation.patch
and it can be found in the queue-4.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Tue Feb 13 17:25:10 CET 2018
From: Robin Murphy <robin.murphy@xxxxxxx>
Date: Mon, 5 Feb 2018 15:34:19 +0000
Subject: [Variant 1/Spectre-v1] arm64: Use pointer masking to limit uaccess speculation
From: Robin Murphy <robin.murphy@xxxxxxx>
Commit 4d8efc2d5ee4 upstream.
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@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/uaccess.h | 26 +++++++++++++++++++++++---
1 file changed, 23 insertions(+), 3 deletions(-)
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -216,6 +216,26 @@ static inline void uaccess_enable_not_ua
}
/*
+ * 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()"
* call.
@@ -285,7 +305,7 @@ 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); \
})
@@ -349,7 +369,7 @@ 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; \
})
@@ -365,7 +385,7 @@ extern unsigned long __must_check __clea
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;
}
Patches currently in stable-queue which might be from robin.murphy@xxxxxxx are
queue-4.15/arm64-make-user_ds-an-inclusive-limit.patch
queue-4.15/arm64-uaccess-don-t-bother-eliding-access_ok-checks-in-__-get-put-_user.patch
queue-4.15/arm-arm64-smccc-make-function-identifiers-an-unsigned-quantity.patch
queue-4.15/firmware-psci-expose-psci-conduit.patch
queue-4.15/firmware-psci-expose-smccc-version-through-psci_ops.patch
queue-4.15/arm64-use-pointer-masking-to-limit-uaccess-speculation.patch
queue-4.15/arm-arm64-smccc-implement-smccc-v1.1-inline-primitive.patch
queue-4.15/arm64-implement-array_index_mask_nospec.patch