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arm64: Add support for PR_SPEC_DISABLE_NOEXEC prctl() option

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The PR_SPEC_DISABLE_NOEXEC option to the PR_SPEC_STORE_BYPASS prctl()
allows the SSB mitigation to be enabled only until the next execve(),
at which point the state will revert back to PR_SPEC_ENABLE and the
mitigation will be disabled.

Add support for PR_SPEC_DISABLE_NOEXEC on arm64.

Reported-by: Anthony Steinhauser <asteinhauser@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Will Deacon 2020-09-28 14:03:00 +01:00
parent 5c8b0cbd9d
commit 780c083a8f
2 changed files with 40 additions and 4 deletions
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6
arch/arm64/kernel/process.c
View File

@ -21,6 +21,7 @@
#include <linux/lockdep.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/nospec.h>
#include <linux/stddef.h>
#include <linux/sysctl.h>
#include <linux/unistd.h>
@ -609,6 +610,11 @@ void arch_setup_new_exec(void)
current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;
ptrauth_thread_init_user(current);
if (task_spec_ssb_noexec(current)) {
arch_prctl_spec_ctrl_set(current, PR_SPEC_STORE_BYPASS,
PR_SPEC_ENABLE);
}
}
#ifdef CONFIG_ARM64_TAGGED_ADDR_ABI

38
arch/arm64/kernel/proton-pack.c
View File

@ -660,6 +660,20 @@ void spectre_v4_enable_task_mitigation(struct task_struct *tsk)
* prctl() may be necessary even when PSTATE.SSBS can be toggled directly
* from userspace.
*/
static void ssbd_prctl_enable_mitigation(struct task_struct *task)
{
task_clear_spec_ssb_noexec(task);
task_set_spec_ssb_disable(task);
set_tsk_thread_flag(task, TIF_SSBD);
}
static void ssbd_prctl_disable_mitigation(struct task_struct *task)
{
task_clear_spec_ssb_noexec(task);
task_clear_spec_ssb_disable(task);
clear_tsk_thread_flag(task, TIF_SSBD);
}
static int ssbd_prctl_set(struct task_struct *task, unsigned long ctrl)
{
switch (ctrl) {
@ -679,8 +693,7 @@ static int ssbd_prctl_set(struct task_struct *task, unsigned long ctrl)
if (spectre_v4_mitigations_on())
return -EPERM;
task_clear_spec_ssb_disable(task);
clear_tsk_thread_flag(task, TIF_SSBD);
ssbd_prctl_disable_mitigation(task);
break;
case PR_SPEC_FORCE_DISABLE:
/* Force disable speculation: force enable mitigation */
@ -699,8 +712,22 @@ static int ssbd_prctl_set(struct task_struct *task, unsigned long ctrl)
if (spectre_v4_mitigations_off())
return -EPERM;
task_set_spec_ssb_disable(task);
set_tsk_thread_flag(task, TIF_SSBD);
ssbd_prctl_enable_mitigation(task);
break;
case PR_SPEC_DISABLE_NOEXEC:
/* Disable speculation until execve(): enable mitigation */
/*
* If the mitigation state is forced one way or the other, then
* we must fail now before we try to toggle it on execve().
*/
if (task_spec_ssb_force_disable(task) ||
spectre_v4_mitigations_off() ||
spectre_v4_mitigations_on()) {
return -EPERM;
}
ssbd_prctl_enable_mitigation(task);
task_set_spec_ssb_noexec(task);
break;
default:
return -ERANGE;
@ -745,6 +772,9 @@ static int ssbd_prctl_get(struct task_struct *task)
if (task_spec_ssb_force_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;
if (task_spec_ssb_noexec(task))
return PR_SPEC_PRCTL | PR_SPEC_DISABLE_NOEXEC;
if (task_spec_ssb_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_DISABLE;