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| author | Marc Zyngier <marc.zyngier@arm.com> | 2019-07-22 14:53:09 +0100 |
|---|---|---|
| committer | Will Deacon <will@kernel.org> | 2019-07-22 15:24:16 +0100 |
| commit | cbdf8a189a66001c36007bf0f5c975d0376c5c3a (patch) | |
| tree | 04692e85f7d27e7ff4c6c07aed2905a1d6b7112d /arch | |
| parent | 4574b0b9abc83a3522b2e91c43b9f0c479855d3a (diff) | |
| download | linux-cbdf8a189a66001c36007bf0f5c975d0376c5c3a.tar.bz2 | |
arm64: Force SSBS on context switch
On a CPU that doesn't support SSBS, PSTATE[12] is RES0. In a system
where only some of the CPUs implement SSBS, we end-up losing track of
the SSBS bit across task migration.
To address this issue, let's force the SSBS bit on context switch.
Fixes: 8f04e8e6e29c ("arm64: ssbd: Add support for PSTATE.SSBS rather than trapping to EL3")
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
[will: inverted logic and added comments]
Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/arm64/include/asm/processor.h | 14 | ||||
| -rw-r--r-- | arch/arm64/kernel/process.c | 29 |
2 files changed, 40 insertions, 3 deletions
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index fd5b1a4efc70..844e2964b0f5 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -193,6 +193,16 @@ static inline void start_thread_common(struct pt_regs *regs, unsigned long pc) regs->pmr_save = GIC_PRIO_IRQON; } +static inline void set_ssbs_bit(struct pt_regs *regs) +{ + regs->pstate |= PSR_SSBS_BIT; +} + +static inline void set_compat_ssbs_bit(struct pt_regs *regs) +{ + regs->pstate |= PSR_AA32_SSBS_BIT; +} + static inline void start_thread(struct pt_regs *regs, unsigned long pc, unsigned long sp) { @@ -200,7 +210,7 @@ static inline void start_thread(struct pt_regs *regs, unsigned long pc, regs->pstate = PSR_MODE_EL0t; if (arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE) - regs->pstate |= PSR_SSBS_BIT; + set_ssbs_bit(regs); regs->sp = sp; } @@ -219,7 +229,7 @@ static inline void compat_start_thread(struct pt_regs *regs, unsigned long pc, #endif if (arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE) - regs->pstate |= PSR_AA32_SSBS_BIT; + set_compat_ssbs_bit(regs); regs->compat_sp = sp; } diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 8d836d0abc96..f674f28df663 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -398,7 +398,7 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, childregs->pstate |= PSR_UAO_BIT; if (arm64_get_ssbd_state() == ARM64_SSBD_FORCE_DISABLE) - childregs->pstate |= PSR_SSBS_BIT; + set_ssbs_bit(childregs); if (system_uses_irq_prio_masking()) childregs->pmr_save = GIC_PRIO_IRQON; @@ -443,6 +443,32 @@ void uao_thread_switch(struct task_struct *next) } /* + * Force SSBS state on context-switch, since it may be lost after migrating + * from a CPU which treats the bit as RES0 in a heterogeneous system. + */ +static void ssbs_thread_switch(struct task_struct *next) +{ + struct pt_regs *regs = task_pt_regs(next); + + /* + * Nothing to do for kernel threads, but 'regs' may be junk + * (e.g. idle task) so check the flags and bail early. + */ + if (unlikely(next->flags & PF_KTHREAD)) + return; + + /* If the mitigation is enabled, then we leave SSBS clear. */ + if ((arm64_get_ssbd_state() == ARM64_SSBD_FORCE_ENABLE) || + test_tsk_thread_flag(next, TIF_SSBD)) + return; + + if (compat_user_mode(regs)) + set_compat_ssbs_bit(regs); + else if (user_mode(regs)) + set_ssbs_bit(regs); +} + +/* * We store our current task in sp_el0, which is clobbered by userspace. Keep a * shadow copy so that we can restore this upon entry from userspace. * @@ -471,6 +497,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev, entry_task_switch(next); uao_thread_switch(next); ptrauth_thread_switch(next); + ssbs_thread_switch(next); /* * Complete any pending TLB or cache maintenance on this CPU in case |