* [PATCH] arm64: Explicitly set pstate.ssbs for el0 on kernel entry @ 2019-07-09 11:22 Neeraj Upadhyay 2019-07-09 13:08 ` Marc Zyngier 0 siblings, 1 reply; 6+ messages in thread From: Neeraj Upadhyay @ 2019-07-09 11:22 UTC (permalink / raw) To: will, mark.rutland, marc.zyngier, julien.thierry, tglx Cc: linux-arm-kernel, linux-kernel, linux-arm-msm, gkohli, parthd, Neeraj Upadhyay For cpus which do not support pstate.ssbs feature, el0 might not retain spsr.ssbs. This is problematic, if this task migrates to a cpu supporting this feature, thus relying on its state to be correct. On kernel entry, explicitly set spsr.ssbs, so that speculation is enabled for el0, when this task migrates to a cpu supporting ssbs feature. Restoring state at kernel entry ensures that el0 ssbs state is always consistent while we are in el1. As alternatives are applied by boot cpu, at the end of smp init, presence/absence of ssbs feature on boot cpu, is used for deciding, whether the capability is uniformly provided. Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> --- arch/arm64/kernel/cpu_errata.c | 16 ++++++++++++++++ arch/arm64/kernel/entry.S | 26 +++++++++++++++++++++++++- 2 files changed, 41 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c index ca11ff7..c84a56d 100644 --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -336,6 +336,22 @@ void __init arm64_enable_wa2_handling(struct alt_instr *alt, *updptr = cpu_to_le32(aarch64_insn_gen_nop()); } +void __init arm64_restore_ssbs_state(struct alt_instr *alt, + __le32 *origptr, __le32 *updptr, + int nr_inst) +{ + BUG_ON(nr_inst != 1); + /* + * Only restore EL0 SSBS state on EL1 entry if cpu does not + * support the capability and capability is present for at + * least one cpu and if the SSBD state allows it to + * be changed. + */ + if (!this_cpu_has_cap(ARM64_SSBS) && cpus_have_cap(ARM64_SSBS) && + arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE) + *updptr = cpu_to_le32(aarch64_insn_gen_nop()); +} + void arm64_set_ssbd_mitigation(bool state) { if (!IS_ENABLED(CONFIG_ARM64_SSBD)) { diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 9cdc459..7e79305 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -143,6 +143,25 @@ alternative_cb_end #endif .endm + // This macro updates spsr. It also corrupts the condition + // codes state. + .macro restore_ssbs_state, saved_spsr, tmp +#ifdef CONFIG_ARM64_SSBD +alternative_cb arm64_restore_ssbs_state + b .L__asm_ssbs_skip\@ +alternative_cb_end + ldr \tmp, [tsk, #TSK_TI_FLAGS] + tbnz \tmp, #TIF_SSBD, .L__asm_ssbs_skip\@ + tst \saved_spsr, #PSR_MODE32_BIT // native task? + b.ne .L__asm_ssbs_compat\@ + orr \saved_spsr, \saved_spsr, #PSR_SSBS_BIT + b .L__asm_ssbs_skip\@ +.L__asm_ssbs_compat\@: + orr \saved_spsr, \saved_spsr, #PSR_AA32_SSBS_BIT +.L__asm_ssbs_skip\@: +#endif + .endm + .macro kernel_entry, el, regsize = 64 .if \regsize == 32 mov w0, w0 // zero upper 32 bits of x0 @@ -182,8 +201,13 @@ alternative_cb_end str x20, [tsk, #TSK_TI_ADDR_LIMIT] /* No need to reset PSTATE.UAO, hardware's already set it to 0 for us */ .endif /* \el == 0 */ - mrs x22, elr_el1 mrs x23, spsr_el1 + + .if \el == 0 + restore_ssbs_state x23, x22 + .endif + + mrs x22, elr_el1 stp lr, x21, [sp, #S_LR] /* -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] arm64: Explicitly set pstate.ssbs for el0 on kernel entry 2019-07-09 11:22 [PATCH] arm64: Explicitly set pstate.ssbs for el0 on kernel entry Neeraj Upadhyay @ 2019-07-09 13:08 ` Marc Zyngier 2019-07-09 13:55 ` Mark Rutland 2019-07-09 14:18 ` Neeraj Upadhyay 0 siblings, 2 replies; 6+ messages in thread From: Marc Zyngier @ 2019-07-09 13:08 UTC (permalink / raw) To: Neeraj Upadhyay, will, mark.rutland, julien.thierry, tglx Cc: linux-arm-kernel, linux-kernel, linux-arm-msm, gkohli, parthd Hi Neeraj, On 09/07/2019 12:22, Neeraj Upadhyay wrote: > For cpus which do not support pstate.ssbs feature, el0 > might not retain spsr.ssbs. This is problematic, if this > task migrates to a cpu supporting this feature, thus > relying on its state to be correct. On kernel entry, > explicitly set spsr.ssbs, so that speculation is enabled > for el0, when this task migrates to a cpu supporting > ssbs feature. Restoring state at kernel entry ensures > that el0 ssbs state is always consistent while we are > in el1. > > As alternatives are applied by boot cpu, at the end of smp > init, presence/absence of ssbs feature on boot cpu, is used > for deciding, whether the capability is uniformly provided. I've seen the same issue, but went for a slightly different approach, see below. > > Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> > --- > arch/arm64/kernel/cpu_errata.c | 16 ++++++++++++++++ > arch/arm64/kernel/entry.S | 26 +++++++++++++++++++++++++- > 2 files changed, 41 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c > index ca11ff7..c84a56d 100644 > --- a/arch/arm64/kernel/cpu_errata.c > +++ b/arch/arm64/kernel/cpu_errata.c > @@ -336,6 +336,22 @@ void __init arm64_enable_wa2_handling(struct alt_instr *alt, > *updptr = cpu_to_le32(aarch64_insn_gen_nop()); > } > > +void __init arm64_restore_ssbs_state(struct alt_instr *alt, > + __le32 *origptr, __le32 *updptr, > + int nr_inst) > +{ > + BUG_ON(nr_inst != 1); > + /* > + * Only restore EL0 SSBS state on EL1 entry if cpu does not > + * support the capability and capability is present for at > + * least one cpu and if the SSBD state allows it to > + * be changed. > + */ > + if (!this_cpu_has_cap(ARM64_SSBS) && cpus_have_cap(ARM64_SSBS) && > + arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE) > + *updptr = cpu_to_le32(aarch64_insn_gen_nop()); > +} > + > void arm64_set_ssbd_mitigation(bool state) > { > if (!IS_ENABLED(CONFIG_ARM64_SSBD)) { > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 9cdc459..7e79305 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -143,6 +143,25 @@ alternative_cb_end > #endif > .endm > > + // This macro updates spsr. It also corrupts the condition > + // codes state. > + .macro restore_ssbs_state, saved_spsr, tmp > +#ifdef CONFIG_ARM64_SSBD > +alternative_cb arm64_restore_ssbs_state > + b .L__asm_ssbs_skip\@ > +alternative_cb_end > + ldr \tmp, [tsk, #TSK_TI_FLAGS] > + tbnz \tmp, #TIF_SSBD, .L__asm_ssbs_skip\@ > + tst \saved_spsr, #PSR_MODE32_BIT // native task? > + b.ne .L__asm_ssbs_compat\@ > + orr \saved_spsr, \saved_spsr, #PSR_SSBS_BIT > + b .L__asm_ssbs_skip\@ > +.L__asm_ssbs_compat\@: > + orr \saved_spsr, \saved_spsr, #PSR_AA32_SSBS_BIT > +.L__asm_ssbs_skip\@: > +#endif > + .endm Although this is in keeping with the rest of entry.S (perfectly unreadable ;-), I think we can do something a bit simpler, that doesn't rely on patching. Also, this doesn't seem to take the SSBD options such as ARM64_SSBD_FORCE_ENABLE into account. > + > .macro kernel_entry, el, regsize = 64 > .if \regsize == 32 > mov w0, w0 // zero upper 32 bits of x0 > @@ -182,8 +201,13 @@ alternative_cb_end > str x20, [tsk, #TSK_TI_ADDR_LIMIT] > /* No need to reset PSTATE.UAO, hardware's already set it to 0 for us */ > .endif /* \el == 0 */ > - mrs x22, elr_el1 > mrs x23, spsr_el1 > + > + .if \el == 0 > + restore_ssbs_state x23, x22 > + .endif > + > + mrs x22, elr_el1 > stp lr, x21, [sp, #S_LR] > > /* > How about the patch below? Thanks, M. From 7d4314d1ef3122d8bf56a7ef239c8c68e0c81277 Mon Sep 17 00:00:00 2001 From: Marc Zyngier <marc.zyngier@arm.com> Date: Tue, 4 Jun 2019 17:35:18 +0100 Subject: [PATCH] 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. Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> --- arch/arm64/include/asm/processor.h | 14 ++++++++++++-- arch/arm64/kernel/process.c | 14 ++++++++++++++ 2 files changed, 26 insertions(+), 2 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 9856395ccdb7..d451b3b248cf 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -442,6 +442,19 @@ void uao_thread_switch(struct task_struct *next) } } +static void ssbs_thread_switch(struct task_struct *next) +{ + if (arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE && + !test_tsk_thread_flag(next, TIF_SSBD)) { + struct pt_regs *regs = task_pt_regs(next); + + 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 +484,7 @@ __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 -- 2.20.1 -- Jazz is not dead. It just smells funny... ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] arm64: Explicitly set pstate.ssbs for el0 on kernel entry 2019-07-09 13:08 ` Marc Zyngier @ 2019-07-09 13:55 ` Mark Rutland 2019-07-09 14:18 ` Neeraj Upadhyay 1 sibling, 0 replies; 6+ messages in thread From: Mark Rutland @ 2019-07-09 13:55 UTC (permalink / raw) To: Marc Zyngier Cc: Neeraj Upadhyay, will, julien.thierry, tglx, linux-arm-kernel, linux-kernel, linux-arm-msm, gkohli, parthd Hi Marc, On Tue, Jul 09, 2019 at 02:08:28PM +0100, Marc Zyngier wrote: > From 7d4314d1ef3122d8bf56a7ef239c8c68e0c81277 Mon Sep 17 00:00:00 2001 > From: Marc Zyngier <marc.zyngier@arm.com> > Date: Tue, 4 Jun 2019 17:35:18 +0100 > Subject: [PATCH] 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. > > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> > --- > arch/arm64/include/asm/processor.h | 14 ++++++++++++-- > arch/arm64/kernel/process.c | 14 ++++++++++++++ > 2 files changed, 26 insertions(+), 2 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 9856395ccdb7..d451b3b248cf 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -442,6 +442,19 @@ void uao_thread_switch(struct task_struct *next) > } > } > > +static void ssbs_thread_switch(struct task_struct *next) > +{ > + if (arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE && > + !test_tsk_thread_flag(next, TIF_SSBD)) { > + struct pt_regs *regs = task_pt_regs(next); > + > + if (compat_user_mode(regs)) > + set_compat_ssbs_bit(regs); > + else if (user_mode(regs)) > + set_ssbs_bit(regs); > + } > +} I think this isn't quite right, and it's not always safe to call task_pt_regs() on a task. For user tasks, the kernel stack looks like: +---------+ <=== task_stack_page(tsk) + THREAD_SIZE; | | | pt_regs | | | +---------+ <=== task_pt_regs(tsk) | | | | | | | stack | | | | | | | +---------+ <=== task_stack_page(tsk) ... where: #define task_pt_regs(p) \ ((struct pt_regs *)(THREAD_SIZE + task_stack_page(p)) - 1) ... and in copy_thread() we initialize a new tsk's SP to start at task_pt_regs(tsk). However, in __cpu_up() we start the idle threads stacks without the pt_regs bias, at task_stack_page(tsk) + THREAD_SIZE. Likewise for the initial thread in __primary_switched(). So task_pt_regs(idle) will return an aliasing portion of stack, rather than a pt_regs. So when switching to those, we'll look at unrelated stack, and corrupt it. We could add a pt_regs bias to those to prevent stack corruption, though assuming stacks are zero-initialized, user_mode(task_pt_regs(tsk)) should always be true, since: #define PSR_MODE_EL0t 0x00000000 #define user_mode(regs) \ (((regs)->pstate & PSR_MODE_MASK) == PSR_MODE_EL0t) We could: (a) Check for PF_KTRHEAD in ssbs_thread_switch(), and skip when this is set. (b) Add the pt_regs bias to all stacks, and not care about the pointless manipulation of the junk regs. (c) Make task_pt_regs() return NULL for kthreads, and fix up the fallout. I'm very tempted to do this longer term even if we do (a) or (b) for now. Thanks, Mark. ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] arm64: Explicitly set pstate.ssbs for el0 on kernel entry 2019-07-09 13:08 ` Marc Zyngier 2019-07-09 13:55 ` Mark Rutland @ 2019-07-09 14:18 ` Neeraj Upadhyay 2019-07-09 14:22 ` Marc Zyngier 1 sibling, 1 reply; 6+ messages in thread From: Neeraj Upadhyay @ 2019-07-09 14:18 UTC (permalink / raw) To: Marc Zyngier, will, mark.rutland, julien.thierry, tglx Cc: linux-arm-kernel, linux-kernel, linux-arm-msm, gkohli, parthd Hi Marc, On 7/9/19 6:38 PM, Marc Zyngier wrote: > Hi Neeraj, > > On 09/07/2019 12:22, Neeraj Upadhyay wrote: >> For cpus which do not support pstate.ssbs feature, el0 >> might not retain spsr.ssbs. This is problematic, if this >> task migrates to a cpu supporting this feature, thus >> relying on its state to be correct. On kernel entry, >> explicitly set spsr.ssbs, so that speculation is enabled >> for el0, when this task migrates to a cpu supporting >> ssbs feature. Restoring state at kernel entry ensures >> that el0 ssbs state is always consistent while we are >> in el1. >> >> As alternatives are applied by boot cpu, at the end of smp >> init, presence/absence of ssbs feature on boot cpu, is used >> for deciding, whether the capability is uniformly provided. > I've seen the same issue, but went for a slightly different > approach, see below. > >> Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> >> --- >> arch/arm64/kernel/cpu_errata.c | 16 ++++++++++++++++ >> arch/arm64/kernel/entry.S | 26 +++++++++++++++++++++++++- >> 2 files changed, 41 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c >> index ca11ff7..c84a56d 100644 >> --- a/arch/arm64/kernel/cpu_errata.c >> +++ b/arch/arm64/kernel/cpu_errata.c >> @@ -336,6 +336,22 @@ void __init arm64_enable_wa2_handling(struct alt_instr *alt, >> *updptr = cpu_to_le32(aarch64_insn_gen_nop()); >> } >> >> +void __init arm64_restore_ssbs_state(struct alt_instr *alt, >> + __le32 *origptr, __le32 *updptr, >> + int nr_inst) >> +{ >> + BUG_ON(nr_inst != 1); >> + /* >> + * Only restore EL0 SSBS state on EL1 entry if cpu does not >> + * support the capability and capability is present for at >> + * least one cpu and if the SSBD state allows it to >> + * be changed. >> + */ >> + if (!this_cpu_has_cap(ARM64_SSBS) && cpus_have_cap(ARM64_SSBS) && >> + arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE) >> + *updptr = cpu_to_le32(aarch64_insn_gen_nop()); >> +} >> + >> void arm64_set_ssbd_mitigation(bool state) >> { >> if (!IS_ENABLED(CONFIG_ARM64_SSBD)) { >> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S >> index 9cdc459..7e79305 100644 >> --- a/arch/arm64/kernel/entry.S >> +++ b/arch/arm64/kernel/entry.S >> @@ -143,6 +143,25 @@ alternative_cb_end >> #endif >> .endm >> >> + // This macro updates spsr. It also corrupts the condition >> + // codes state. >> + .macro restore_ssbs_state, saved_spsr, tmp >> +#ifdef CONFIG_ARM64_SSBD >> +alternative_cb arm64_restore_ssbs_state >> + b .L__asm_ssbs_skip\@ >> +alternative_cb_end >> + ldr \tmp, [tsk, #TSK_TI_FLAGS] >> + tbnz \tmp, #TIF_SSBD, .L__asm_ssbs_skip\@ >> + tst \saved_spsr, #PSR_MODE32_BIT // native task? >> + b.ne .L__asm_ssbs_compat\@ >> + orr \saved_spsr, \saved_spsr, #PSR_SSBS_BIT >> + b .L__asm_ssbs_skip\@ >> +.L__asm_ssbs_compat\@: >> + orr \saved_spsr, \saved_spsr, #PSR_AA32_SSBS_BIT >> +.L__asm_ssbs_skip\@: >> +#endif >> + .endm > Although this is in keeping with the rest of entry.S (perfectly > unreadable ;-), I think we can do something a bit simpler, that > doesn't rely on patching. Also, this doesn't seem to take the > SSBD options such as ARM64_SSBD_FORCE_ENABLE into account. arm64_restore_ssbs_state has a check for ARM64_SSBD_FORCE_ENABLE, does that look wrong? > >> + >> .macro kernel_entry, el, regsize = 64 >> .if \regsize == 32 >> mov w0, w0 // zero upper 32 bits of x0 >> @@ -182,8 +201,13 @@ alternative_cb_end >> str x20, [tsk, #TSK_TI_ADDR_LIMIT] >> /* No need to reset PSTATE.UAO, hardware's already set it to 0 for us */ >> .endif /* \el == 0 */ >> - mrs x22, elr_el1 >> mrs x23, spsr_el1 >> + >> + .if \el == 0 >> + restore_ssbs_state x23, x22 >> + .endif >> + >> + mrs x22, elr_el1 >> stp lr, x21, [sp, #S_LR] >> >> /* >> > How about the patch below? Looks good; was just going to mention PF_KTHREAD check, but Mark R. has already given detailed information about it. Thanks Neeraj > > Thanks, > > M. > > From 7d4314d1ef3122d8bf56a7ef239c8c68e0c81277 Mon Sep 17 00:00:00 2001 > From: Marc Zyngier <marc.zyngier@arm.com> > Date: Tue, 4 Jun 2019 17:35:18 +0100 > Subject: [PATCH] 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. > > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> > --- > arch/arm64/include/asm/processor.h | 14 ++++++++++++-- > arch/arm64/kernel/process.c | 14 ++++++++++++++ > 2 files changed, 26 insertions(+), 2 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 9856395ccdb7..d451b3b248cf 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -442,6 +442,19 @@ void uao_thread_switch(struct task_struct *next) > } > } > > +static void ssbs_thread_switch(struct task_struct *next) > +{ > + if (arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE && > + !test_tsk_thread_flag(next, TIF_SSBD)) { > + struct pt_regs *regs = task_pt_regs(next); > + > + 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 +484,7 @@ __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 -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] arm64: Explicitly set pstate.ssbs for el0 on kernel entry 2019-07-09 14:18 ` Neeraj Upadhyay @ 2019-07-09 14:22 ` Marc Zyngier 2019-07-19 4:53 ` Neeraj Upadhyay 0 siblings, 1 reply; 6+ messages in thread From: Marc Zyngier @ 2019-07-09 14:22 UTC (permalink / raw) To: Neeraj Upadhyay, will, mark.rutland, julien.thierry, tglx Cc: linux-arm-kernel, linux-kernel, linux-arm-msm, gkohli, parthd On 09/07/2019 15:18, Neeraj Upadhyay wrote: > Hi Marc, > > On 7/9/19 6:38 PM, Marc Zyngier wrote: >> Hi Neeraj, >> >> On 09/07/2019 12:22, Neeraj Upadhyay wrote: >>> For cpus which do not support pstate.ssbs feature, el0 >>> might not retain spsr.ssbs. This is problematic, if this >>> task migrates to a cpu supporting this feature, thus >>> relying on its state to be correct. On kernel entry, >>> explicitly set spsr.ssbs, so that speculation is enabled >>> for el0, when this task migrates to a cpu supporting >>> ssbs feature. Restoring state at kernel entry ensures >>> that el0 ssbs state is always consistent while we are >>> in el1. >>> >>> As alternatives are applied by boot cpu, at the end of smp >>> init, presence/absence of ssbs feature on boot cpu, is used >>> for deciding, whether the capability is uniformly provided. >> I've seen the same issue, but went for a slightly different >> approach, see below. >> >>> Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> >>> --- >>> arch/arm64/kernel/cpu_errata.c | 16 ++++++++++++++++ >>> arch/arm64/kernel/entry.S | 26 +++++++++++++++++++++++++- >>> 2 files changed, 41 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c >>> index ca11ff7..c84a56d 100644 >>> --- a/arch/arm64/kernel/cpu_errata.c >>> +++ b/arch/arm64/kernel/cpu_errata.c >>> @@ -336,6 +336,22 @@ void __init arm64_enable_wa2_handling(struct alt_instr *alt, >>> *updptr = cpu_to_le32(aarch64_insn_gen_nop()); >>> } >>> >>> +void __init arm64_restore_ssbs_state(struct alt_instr *alt, >>> + __le32 *origptr, __le32 *updptr, >>> + int nr_inst) >>> +{ >>> + BUG_ON(nr_inst != 1); >>> + /* >>> + * Only restore EL0 SSBS state on EL1 entry if cpu does not >>> + * support the capability and capability is present for at >>> + * least one cpu and if the SSBD state allows it to >>> + * be changed. >>> + */ >>> + if (!this_cpu_has_cap(ARM64_SSBS) && cpus_have_cap(ARM64_SSBS) && >>> + arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE) >>> + *updptr = cpu_to_le32(aarch64_insn_gen_nop()); >>> +} >>> + >>> void arm64_set_ssbd_mitigation(bool state) >>> { >>> if (!IS_ENABLED(CONFIG_ARM64_SSBD)) { >>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S >>> index 9cdc459..7e79305 100644 >>> --- a/arch/arm64/kernel/entry.S >>> +++ b/arch/arm64/kernel/entry.S >>> @@ -143,6 +143,25 @@ alternative_cb_end >>> #endif >>> .endm >>> >>> + // This macro updates spsr. It also corrupts the condition >>> + // codes state. >>> + .macro restore_ssbs_state, saved_spsr, tmp >>> +#ifdef CONFIG_ARM64_SSBD >>> +alternative_cb arm64_restore_ssbs_state >>> + b .L__asm_ssbs_skip\@ >>> +alternative_cb_end >>> + ldr \tmp, [tsk, #TSK_TI_FLAGS] >>> + tbnz \tmp, #TIF_SSBD, .L__asm_ssbs_skip\@ >>> + tst \saved_spsr, #PSR_MODE32_BIT // native task? >>> + b.ne .L__asm_ssbs_compat\@ >>> + orr \saved_spsr, \saved_spsr, #PSR_SSBS_BIT >>> + b .L__asm_ssbs_skip\@ >>> +.L__asm_ssbs_compat\@: >>> + orr \saved_spsr, \saved_spsr, #PSR_AA32_SSBS_BIT >>> +.L__asm_ssbs_skip\@: >>> +#endif >>> + .endm >> Although this is in keeping with the rest of entry.S (perfectly >> unreadable ;-), I think we can do something a bit simpler, that >> doesn't rely on patching. Also, this doesn't seem to take the >> SSBD options such as ARM64_SSBD_FORCE_ENABLE into account. > > arm64_restore_ssbs_state has a check for ARM64_SSBD_FORCE_ENABLE, > > does that look wrong? No, I just focused on the rest of the asm code and missed it, apologies. > >> >>> + >>> .macro kernel_entry, el, regsize = 64 >>> .if \regsize == 32 >>> mov w0, w0 // zero upper 32 bits of x0 >>> @@ -182,8 +201,13 @@ alternative_cb_end >>> str x20, [tsk, #TSK_TI_ADDR_LIMIT] >>> /* No need to reset PSTATE.UAO, hardware's already set it to 0 for us */ >>> .endif /* \el == 0 */ >>> - mrs x22, elr_el1 >>> mrs x23, spsr_el1 >>> + >>> + .if \el == 0 >>> + restore_ssbs_state x23, x22 >>> + .endif >>> + >>> + mrs x22, elr_el1 >>> stp lr, x21, [sp, #S_LR] >>> >>> /* >>> >> How about the patch below? > > Looks good; was just going to mention PF_KTHREAD check, but Mark R. has > already > > given detailed information about it. Yup, well spotted. I'll respin it shortly and we can then work out whether that's really a better approach. Thanks, M. -- Jazz is not dead. It just smells funny... ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] arm64: Explicitly set pstate.ssbs for el0 on kernel entry 2019-07-09 14:22 ` Marc Zyngier @ 2019-07-19 4:53 ` Neeraj Upadhyay 0 siblings, 0 replies; 6+ messages in thread From: Neeraj Upadhyay @ 2019-07-19 4:53 UTC (permalink / raw) To: Marc Zyngier, will, mark.rutland, julien.thierry, tglx Cc: linux-arm-kernel, linux-kernel, linux-arm-msm, gkohli, parthd, tsoni Hi Marc, On 7/9/19 7:52 PM, Marc Zyngier wrote: > On 09/07/2019 15:18, Neeraj Upadhyay wrote: >> Hi Marc, >> >> On 7/9/19 6:38 PM, Marc Zyngier wrote: >>> Hi Neeraj, >>> >>> On 09/07/2019 12:22, Neeraj Upadhyay wrote: >>>> For cpus which do not support pstate.ssbs feature, el0 >>>> might not retain spsr.ssbs. This is problematic, if this >>>> task migrates to a cpu supporting this feature, thus >>>> relying on its state to be correct. On kernel entry, >>>> explicitly set spsr.ssbs, so that speculation is enabled >>>> for el0, when this task migrates to a cpu supporting >>>> ssbs feature. Restoring state at kernel entry ensures >>>> that el0 ssbs state is always consistent while we are >>>> in el1. >>>> >>>> As alternatives are applied by boot cpu, at the end of smp >>>> init, presence/absence of ssbs feature on boot cpu, is used >>>> for deciding, whether the capability is uniformly provided. >>> I've seen the same issue, but went for a slightly different >>> approach, see below. >>> >>>> Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> >>>> --- >>>> arch/arm64/kernel/cpu_errata.c | 16 ++++++++++++++++ >>>> arch/arm64/kernel/entry.S | 26 +++++++++++++++++++++++++- >>>> 2 files changed, 41 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c >>>> index ca11ff7..c84a56d 100644 >>>> --- a/arch/arm64/kernel/cpu_errata.c >>>> +++ b/arch/arm64/kernel/cpu_errata.c >>>> @@ -336,6 +336,22 @@ void __init arm64_enable_wa2_handling(struct alt_instr *alt, >>>> *updptr = cpu_to_le32(aarch64_insn_gen_nop()); >>>> } >>>> >>>> +void __init arm64_restore_ssbs_state(struct alt_instr *alt, >>>> + __le32 *origptr, __le32 *updptr, >>>> + int nr_inst) >>>> +{ >>>> + BUG_ON(nr_inst != 1); >>>> + /* >>>> + * Only restore EL0 SSBS state on EL1 entry if cpu does not >>>> + * support the capability and capability is present for at >>>> + * least one cpu and if the SSBD state allows it to >>>> + * be changed. >>>> + */ >>>> + if (!this_cpu_has_cap(ARM64_SSBS) && cpus_have_cap(ARM64_SSBS) && >>>> + arm64_get_ssbd_state() != ARM64_SSBD_FORCE_ENABLE) >>>> + *updptr = cpu_to_le32(aarch64_insn_gen_nop()); >>>> +} >>>> + >>>> void arm64_set_ssbd_mitigation(bool state) >>>> { >>>> if (!IS_ENABLED(CONFIG_ARM64_SSBD)) { >>>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S >>>> index 9cdc459..7e79305 100644 >>>> --- a/arch/arm64/kernel/entry.S >>>> +++ b/arch/arm64/kernel/entry.S >>>> @@ -143,6 +143,25 @@ alternative_cb_end >>>> #endif >>>> .endm >>>> >>>> + // This macro updates spsr. It also corrupts the condition >>>> + // codes state. >>>> + .macro restore_ssbs_state, saved_spsr, tmp >>>> +#ifdef CONFIG_ARM64_SSBD >>>> +alternative_cb arm64_restore_ssbs_state >>>> + b .L__asm_ssbs_skip\@ >>>> +alternative_cb_end >>>> + ldr \tmp, [tsk, #TSK_TI_FLAGS] >>>> + tbnz \tmp, #TIF_SSBD, .L__asm_ssbs_skip\@ >>>> + tst \saved_spsr, #PSR_MODE32_BIT // native task? >>>> + b.ne .L__asm_ssbs_compat\@ >>>> + orr \saved_spsr, \saved_spsr, #PSR_SSBS_BIT >>>> + b .L__asm_ssbs_skip\@ >>>> +.L__asm_ssbs_compat\@: >>>> + orr \saved_spsr, \saved_spsr, #PSR_AA32_SSBS_BIT >>>> +.L__asm_ssbs_skip\@: >>>> +#endif >>>> + .endm >>> Although this is in keeping with the rest of entry.S (perfectly >>> unreadable ;-), I think we can do something a bit simpler, that >>> doesn't rely on patching. Also, this doesn't seem to take the >>> SSBD options such as ARM64_SSBD_FORCE_ENABLE into account. >> arm64_restore_ssbs_state has a check for ARM64_SSBD_FORCE_ENABLE, >> >> does that look wrong? > No, I just focused on the rest of the asm code and missed it, apologies. > >>>> + >>>> .macro kernel_entry, el, regsize = 64 >>>> .if \regsize == 32 >>>> mov w0, w0 // zero upper 32 bits of x0 >>>> @@ -182,8 +201,13 @@ alternative_cb_end >>>> str x20, [tsk, #TSK_TI_ADDR_LIMIT] >>>> /* No need to reset PSTATE.UAO, hardware's already set it to 0 for us */ >>>> .endif /* \el == 0 */ >>>> - mrs x22, elr_el1 >>>> mrs x23, spsr_el1 >>>> + >>>> + .if \el == 0 >>>> + restore_ssbs_state x23, x22 >>>> + .endif >>>> + >>>> + mrs x22, elr_el1 >>>> stp lr, x21, [sp, #S_LR] >>>> >>>> /* >>>> >>> How about the patch below? >> Looks good; was just going to mention PF_KTHREAD check, but Mark R. has >> already >> >> given detailed information about it. > Yup, well spotted. I'll respin it shortly and we can then work out > whether that's really a better approach. Did you get chance to recheck it? Thanks Neeraj > > Thanks, > > M. -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-07-19 4:53 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-07-09 11:22 [PATCH] arm64: Explicitly set pstate.ssbs for el0 on kernel entry Neeraj Upadhyay 2019-07-09 13:08 ` Marc Zyngier 2019-07-09 13:55 ` Mark Rutland 2019-07-09 14:18 ` Neeraj Upadhyay 2019-07-09 14:22 ` Marc Zyngier 2019-07-19 4:53 ` Neeraj Upadhyay
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