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linux/arch/arm64/kernel/pointer_auth.c

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arm64: add prctl control for resetting ptrauth keys Add an arm64-specific prctl to allow a thread to reinitialize its pointer authentication keys to random values. This can be useful when exec() is not used for starting new processes, to ensure that different processes still have different keys. Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-12-08 02:39:28 +08:00
// SPDX-License-Identifier: GPL-2.0
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>
2020-10-14 13:24:30 +08:00
#include <linux/compat.h>
arm64: add prctl control for resetting ptrauth keys Add an arm64-specific prctl to allow a thread to reinitialize its pointer authentication keys to random values. This can be useful when exec() is not used for starting new processes, to ensure that different processes still have different keys. Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-12-08 02:39:28 +08:00
#include <linux/errno.h>
#include <linux/prctl.h>
#include <linux/random.h>
#include <linux/sched.h>
#include <asm/cpufeature.h>
#include <asm/pointer_auth.h>
int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg)
{
arm64: rename ptrauth key structures to be user-specific We currently enable ptrauth for userspace, but do not use it within the kernel. We're going to enable it for the kernel, and will need to manage a separate set of ptrauth keys for the kernel. We currently keep all 5 keys in struct ptrauth_keys. However, as the kernel will only need to use 1 key, it is a bit wasteful to allocate a whole ptrauth_keys struct for every thread. Therefore, a subsequent patch will define a separate struct, with only 1 key, for the kernel. In preparation for that, rename the existing struct (and associated macros and functions) to reflect that they are specific to userspace. Acked-by: Catalin Marinas <catalin.marinas@arm.com> Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com> Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com> [Amit: Re-positioned the patch to reduce the diff] Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2020-03-13 17:04:50 +08:00
struct ptrauth_keys_user *keys = &tsk->thread.keys_user;
arm64: add prctl control for resetting ptrauth keys Add an arm64-specific prctl to allow a thread to reinitialize its pointer authentication keys to random values. This can be useful when exec() is not used for starting new processes, to ensure that different processes still have different keys. Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-12-08 02:39:28 +08:00
unsigned long addr_key_mask = PR_PAC_APIAKEY | PR_PAC_APIBKEY |
PR_PAC_APDAKEY | PR_PAC_APDBKEY;
unsigned long key_mask = addr_key_mask | PR_PAC_APGAKEY;
if (!system_supports_address_auth() && !system_supports_generic_auth())
return -EINVAL;
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>
2020-10-14 13:24:30 +08:00
if (is_compat_thread(task_thread_info(tsk)))
return -EINVAL;
arm64: add prctl control for resetting ptrauth keys Add an arm64-specific prctl to allow a thread to reinitialize its pointer authentication keys to random values. This can be useful when exec() is not used for starting new processes, to ensure that different processes still have different keys. Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-12-08 02:39:28 +08:00
if (!arg) {
arm64: rename ptrauth key structures to be user-specific We currently enable ptrauth for userspace, but do not use it within the kernel. We're going to enable it for the kernel, and will need to manage a separate set of ptrauth keys for the kernel. We currently keep all 5 keys in struct ptrauth_keys. However, as the kernel will only need to use 1 key, it is a bit wasteful to allocate a whole ptrauth_keys struct for every thread. Therefore, a subsequent patch will define a separate struct, with only 1 key, for the kernel. In preparation for that, rename the existing struct (and associated macros and functions) to reflect that they are specific to userspace. Acked-by: Catalin Marinas <catalin.marinas@arm.com> Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com> Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com> [Amit: Re-positioned the patch to reduce the diff] Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2020-03-13 17:04:50 +08:00
ptrauth_keys_init_user(keys);
arm64: add prctl control for resetting ptrauth keys Add an arm64-specific prctl to allow a thread to reinitialize its pointer authentication keys to random values. This can be useful when exec() is not used for starting new processes, to ensure that different processes still have different keys. Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-12-08 02:39:28 +08:00
return 0;
}
if (arg & ~key_mask)
return -EINVAL;
if (((arg & addr_key_mask) && !system_supports_address_auth()) ||
((arg & PR_PAC_APGAKEY) && !system_supports_generic_auth()))
return -EINVAL;
if (arg & PR_PAC_APIAKEY)
get_random_bytes(&keys->apia, sizeof(keys->apia));
if (arg & PR_PAC_APIBKEY)
get_random_bytes(&keys->apib, sizeof(keys->apib));
if (arg & PR_PAC_APDAKEY)
get_random_bytes(&keys->apda, sizeof(keys->apda));
if (arg & PR_PAC_APDBKEY)
get_random_bytes(&keys->apdb, sizeof(keys->apdb));
if (arg & PR_PAC_APGAKEY)
get_random_bytes(&keys->apga, sizeof(keys->apga));
arm64: pac: Optimize kernel entry/exit key installation code paths The kernel does not use any keys besides IA so we don't need to install IB/DA/DB/GA on kernel exit if we arrange to install them on task switch instead, which we can expect to happen an order of magnitude less often. Furthermore we can avoid installing the user IA in the case where the user task has IA disabled and just leave the kernel IA installed. This also lets us avoid needing to install IA on kernel entry. On an Apple M1 under a hypervisor, the overhead of kernel entry/exit has been measured to be reduced by 15.6ns in the case where IA is enabled, and 31.9ns in the case where IA is disabled. Signed-off-by: Peter Collingbourne <pcc@google.com> Link: https://linux-review.googlesource.com/id/Ieddf6b580d23c9e0bed45a822dabe72d2ffc9a8e Link: https://lore.kernel.org/r/2d653d055f38f779937f2b92f8ddd5cf9e4af4f4.1616123271.git.pcc@google.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2021-03-19 11:10:54 +08:00
ptrauth_keys_install_user(keys);
arm64: add prctl control for resetting ptrauth keys Add an arm64-specific prctl to allow a thread to reinitialize its pointer authentication keys to random values. This can be useful when exec() is not used for starting new processes, to ensure that different processes still have different keys. Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-12-08 02:39:28 +08:00
return 0;
}
arm64: Introduce prctl(PR_PAC_{SET,GET}_ENABLED_KEYS) This change introduces a prctl that allows the user program to control which PAC keys are enabled in a particular task. The main reason why this is useful is to enable a userspace ABI that uses PAC to sign and authenticate function pointers and other pointers exposed outside of the function, while still allowing binaries conforming to the ABI to interoperate with legacy binaries that do not sign or authenticate pointers. The idea is that a dynamic loader or early startup code would issue this prctl very early after establishing that a process may load legacy binaries, but before executing any PAC instructions. This change adds a small amount of overhead to kernel entry and exit due to additional required instruction sequences. On a DragonBoard 845c (Cortex-A75) with the powersave governor, the overhead of similar instruction sequences was measured as 4.9ns when simulating the common case where IA is left enabled, or 43.7ns when simulating the uncommon case where IA is disabled. These numbers can be seen as the worst case scenario, since in more realistic scenarios a better performing governor would be used and a newer chip would be used that would support PAC unlike Cortex-A75 and would be expected to be faster than Cortex-A75. On an Apple M1 under a hypervisor, the overhead of the entry/exit instruction sequences introduced by this patch was measured as 0.3ns in the case where IA is left enabled, and 33.0ns in the case where IA is disabled. Signed-off-by: Peter Collingbourne <pcc@google.com> Reviewed-by: Dave Martin <Dave.Martin@arm.com> Link: https://linux-review.googlesource.com/id/Ibc41a5e6a76b275efbaa126b31119dc197b927a5 Link: https://lore.kernel.org/r/d6609065f8f40397a4124654eb68c9f490b4d477.1616123271.git.pcc@google.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2021-03-19 11:10:53 +08:00
static u64 arg_to_enxx_mask(unsigned long arg)
{
u64 sctlr_enxx_mask = 0;
WARN_ON(arg & ~PR_PAC_ENABLED_KEYS_MASK);
if (arg & PR_PAC_APIAKEY)
sctlr_enxx_mask |= SCTLR_ELx_ENIA;
if (arg & PR_PAC_APIBKEY)
sctlr_enxx_mask |= SCTLR_ELx_ENIB;
if (arg & PR_PAC_APDAKEY)
sctlr_enxx_mask |= SCTLR_ELx_ENDA;
if (arg & PR_PAC_APDBKEY)
sctlr_enxx_mask |= SCTLR_ELx_ENDB;
return sctlr_enxx_mask;
}
int ptrauth_set_enabled_keys(struct task_struct *tsk, unsigned long keys,
unsigned long enabled)
{
u64 sctlr = tsk->thread.sctlr_user;
if (!system_supports_address_auth())
return -EINVAL;
if (is_compat_thread(task_thread_info(tsk)))
return -EINVAL;
if ((keys & ~PR_PAC_ENABLED_KEYS_MASK) || (enabled & ~keys))
return -EINVAL;
sctlr &= ~arg_to_enxx_mask(keys);
sctlr |= arg_to_enxx_mask(enabled);
if (tsk == current)
set_task_sctlr_el1(sctlr);
else
tsk->thread.sctlr_user = sctlr;
return 0;
}
int ptrauth_get_enabled_keys(struct task_struct *tsk)
{
int retval = 0;
if (!system_supports_address_auth())
return -EINVAL;
if (is_compat_thread(task_thread_info(tsk)))
return -EINVAL;
if (tsk->thread.sctlr_user & SCTLR_ELx_ENIA)
retval |= PR_PAC_APIAKEY;
if (tsk->thread.sctlr_user & SCTLR_ELx_ENIB)
retval |= PR_PAC_APIBKEY;
if (tsk->thread.sctlr_user & SCTLR_ELx_ENDA)
retval |= PR_PAC_APDAKEY;
if (tsk->thread.sctlr_user & SCTLR_ELx_ENDB)
retval |= PR_PAC_APDBKEY;
return retval;
}