[PATCH RFC v9 07/25] arm64: Context-switch POR_EL1
From: Kevin Brodsky <hidden>
Date: 2026-08-18 14:12:09
Also in:
linux-hardening, linux-mm
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
POR_EL1 is about to be used by the kpkeys framework, modifying it for (typically small) sections of code. If an exception occurs during that window and scheduling occurs, we must ensure that POR_EL1 is context-switched as needed (saving the old value and restoring the new one). An ISB is needed to ensure the write takes effect, so we skip it if the new value is the same as the old, like for POR_EL0. Signed-off-by: Kevin Brodsky <redacted> --- arch/arm64/include/asm/processor.h | 1 + arch/arm64/kernel/process.c | 10 ++++++++++ 2 files changed, 11 insertions(+)
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index c2a627f39314..8d7fa479cd36 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h@@ -195,6 +195,7 @@ struct thread_struct { u64 svcr; u64 tpidr2_el0; u64 por_el0; + u64 por_el1; #ifdef CONFIG_ARM64_GCS unsigned int gcs_el0_mode; unsigned int gcs_el0_locked;
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 581f80e9b9b7..1dec143decf1 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c@@ -51,6 +51,7 @@ #include <asm/exec.h> #include <asm/fpsimd.h> #include <asm/gcs.h> +#include <asm/kpkeys.h> #include <asm/mmu_context.h> #include <asm/mpam.h> #include <asm/mte.h>
@@ -431,6 +432,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) ptrauth_thread_init_kernel(p); + if (system_supports_poe()) + p->thread.por_el1 = POR_EL1_INIT; + if (likely(!args->fn)) { *childregs = *current_pt_regs(); childregs->regs[0] = 0;
@@ -681,6 +685,12 @@ static void permission_overlay_switch(struct task_struct *next) * of POR_EL0. */ } + + current->thread.por_el1 = read_sysreg_s(SYS_POR_EL1); + if (current->thread.por_el1 != next->thread.por_el1) { + write_sysreg_s(next->thread.por_el1, SYS_POR_EL1); + isb(); + } } /*
--
2.51.2