arm64: reject prctl(PR_PAC_RESET_KEYS) on compat tasks

It doesn't make sense to issue prctl(PR_PAC_RESET_KEYS) on a
compat task because the 32-bit instruction set does not offer PAuth
instructions. For consistency with other 64-bit only prctls such as
{SET,GET}_TAGGED_ADDR_CTRL, reject the prctl on compat tasks.

Although this is a userspace-visible change, maybe it isn't too late
to make this change given that the hardware isn't available yet and
it's very unlikely that anyone has 32-bit software that actually
depends on this succeeding.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/Ie885a1ff84ab498cc9f62d6451e9f2cfd4b1d06a
Link: https://lore.kernel.org/r/20201014052430.11630-1-pcc@google.com
[will: Do the same for the SVE prctl()s]
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index a6d688c10745385c65f2df3f440e8dcd5024819f..062b21f30f9422aa03d6cf0eb8cc56e2ba8032d9 100644 (file)
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -678,7 +678,7 @@ int sve_set_current_vl(unsigned long arg)
        vl = arg & PR_SVE_VL_LEN_MASK;
        flags = arg & ~vl;
 
-       if (!system_supports_sve())
+       if (!system_supports_sve() || is_compat_task())
                return -EINVAL;
 
        ret = sve_set_vector_length(current, vl, flags);
@@ -691,7 +691,7 @@ int sve_set_current_vl(unsigned long arg)
 /* PR_SVE_GET_VL */
 int sve_get_current_vl(void)
 {
-       if (!system_supports_sve())
+       if (!system_supports_sve() || is_compat_task())
                return -EINVAL;
 
        return sve_prctl_status(0);

diff --git a/arch/arm64/kernel/pointer_auth.c b/arch/arm64/kernel/pointer_auth.c
index 1e77736a4f66e5a2f91e1a5e3b9bcedda2a4b9cb..adb955fd9bdd9812e1ab29ac2735d8ea2b836997 100644 (file)
--- a/arch/arm64/kernel/pointer_auth.c
+++ b/arch/arm64/kernel/pointer_auth.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 
+#include <linux/compat.h>
 #include <linux/errno.h>
 #include <linux/prctl.h>
 #include <linux/random.h>
@@ -17,6 +18,9 @@ int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg)
        if (!system_supports_address_auth() && !system_supports_generic_auth())
                return -EINVAL;
 
+       if (is_compat_thread(task_thread_info(tsk)))
+               return -EINVAL;
+
        if (!arg) {
                ptrauth_keys_init_user(keys);
                return 0;