On 5/3/24 18:31, Joey Gouly wrote:
> POR_EL0 is a register that can be modified by userspace directly,
> so it must be context switched.
>
> Signed-off-by: Joey Gouly <joey.gouly@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> ---
> arch/arm64/include/asm/cpufeature.h | 6 ++++++
> arch/arm64/include/asm/processor.h | 1 +
> arch/arm64/include/asm/sysreg.h | 3 +++
> arch/arm64/kernel/process.c | 28 ++++++++++++++++++++++++++++
> 4 files changed, 38 insertions(+)
>
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 8b904a757bd3..d46aab23e06e 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -832,6 +832,12 @@ static inline bool system_supports_lpa2(void)
> return cpus_have_final_cap(ARM64_HAS_LPA2);
> }
>
> +static inline bool system_supports_poe(void)
> +{
> + return IS_ENABLED(CONFIG_ARM64_POE) &&
CONFIG_ARM64_POE has not been defined/added until now ?
> + alternative_has_cap_unlikely(ARM64_HAS_S1POE);
> +}
> +
> int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);
> bool try_emulate_mrs(struct pt_regs *regs, u32 isn);
>
> diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
> index f77371232d8c..e6376f979273 100644
> --- a/arch/arm64/include/asm/processor.h
> +++ b/arch/arm64/include/asm/processor.h
> @@ -184,6 +184,7 @@ struct thread_struct {
> u64 sctlr_user;
> u64 svcr;
> u64 tpidr2_el0;
> + u64 por_el0;
> };
As there going to be a new config i.e CONFIG_ARM64_POE, should not this
register be wrapped up with #ifdef CONFIG_ARM64_POE as well ? Similarly
access into p->thread.por_el0 should also be conditional on that config.
>
> static inline unsigned int thread_get_vl(struct thread_struct *thread,
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 9e8999592f3a..62c399811dbf 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -1064,6 +1064,9 @@
> #define POE_RXW UL(0x7)
> #define POE_MASK UL(0xf)
>
> +/* Initial value for Permission Overlay Extension for EL0 */
> +#define POR_EL0_INIT POE_RXW
The idea behind POE_RXW as the init value is to be all permissive ?
> +
> #define ARM64_FEATURE_FIELD_BITS 4
>
> /* Defined for compatibility only, do not add new users. */
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 4ae31b7af6c3..0ffaca98bed6 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -271,12 +271,23 @@ static void flush_tagged_addr_state(void)
> clear_thread_flag(TIF_TAGGED_ADDR);
> }
>
> +static void flush_poe(void)
> +{
> + if (!system_supports_poe())
> + return;
> +
> + write_sysreg_s(POR_EL0_INIT, SYS_POR_EL0);
> + /* ISB required for kernel uaccess routines when chaning POR_EL0 */
> + isb();
> +}
> +
> void flush_thread(void)
> {
> fpsimd_flush_thread();
> tls_thread_flush();
> flush_ptrace_hw_breakpoint(current);
> flush_tagged_addr_state();
> + flush_poe();
> }
>
> void arch_release_task_struct(struct task_struct *tsk)
> @@ -371,6 +382,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
> if (system_supports_tpidr2())
> p->thread.tpidr2_el0 = read_sysreg_s(SYS_TPIDR2_EL0);
>
> + if (system_supports_poe())
> + p->thread.por_el0 = read_sysreg_s(SYS_POR_EL0);
> +
> if (stack_start) {
> if (is_compat_thread(task_thread_info(p)))
> childregs->compat_sp = stack_start;
> @@ -495,6 +509,19 @@ static void erratum_1418040_new_exec(void)
> preempt_enable();
> }
>
> +static void permission_overlay_switch(struct task_struct *next)
> +{
> + if (!system_supports_poe())
> + return;
> +
> + current->thread.por_el0 = read_sysreg_s(SYS_POR_EL0);
> + if (current->thread.por_el0 != next->thread.por_el0) {
> + write_sysreg_s(next->thread.por_el0, SYS_POR_EL0);
> + /* ISB required for kernel uaccess routines when chaning POR_EL0 */
> + isb();
> + }
> +}
> +
> /*
> * __switch_to() checks current->thread.sctlr_user as an optimisation. Therefore
> * this function must be called with preemption disabled and the update to
> @@ -530,6 +557,7 @@ struct task_struct *__switch_to(struct task_struct *prev,
> ssbs_thread_switch(next);
> erratum_1418040_thread_switch(next);
> ptrauth_thread_switch_user(next);
> + permission_overlay_switch(next);
>
> /*
> * Complete any pending TLB or cache maintenance on this CPU in case
