[PATCH v4 resend 6/7] arm64/efi: Move uaccess en/disable out of efi_set_pgd()

Ard Biesheuvel
2025-10-15T21:01:09Z

efi_set_pgd() will no longer be called when invoking EFI runtime
services via the efi_rts_wq work queue, but the uaccess en/disable are
still needed when using PAN emulation using TTBR0 switching. So move
these into the callers.

Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm64/include/asm/efi.h | 13 +++----------
arch/arm64/kernel/efi.c | 18 ++++++++++++++++++
2 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
index bcd5622aa096..aa91165ca140 100644
--- a/arch/arm64/include/asm/efi.h
+++ b/arch/arm64/include/asm/efi.h
@@ -126,21 +126,14 @@ static inline void efi_set_pgd(struct mm_struct *mm)
if (mm != current->active_mm) {
/*
* Update the current thread's saved ttbr0 since it is
- * restored as part of a return from exception. Enable
- * access to the valid TTBR0_EL1 and invoke the errata
- * workaround directly since there is no return from
- * exception when invoking the EFI run-time services.
+ * restored as part of a return from exception.
*/
update_saved_ttbr0(current, mm);
- uaccess_ttbr0_enable();
- post_ttbr_update_workaround();
} else {
/*
- * Defer the switch to the current thread's TTBR0_EL1
- * until uaccess_enable(). Restore the current
- * thread's saved ttbr0 corresponding to its active_mm
+ * Restore the current thread's saved ttbr0
+ * corresponding to its active_mm
*/
- uaccess_ttbr0_disable();
update_saved_ttbr0(current, current->active_mm);
}
}
diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index 0094f5938ba6..85f65d5c863c 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -169,12 +169,30 @@ void arch_efi_call_virt_setup(void)
{
efi_runtime_assert_lock_held();
efi_virtmap_load();
+
+ /*
+ * Enable access to the valid TTBR0_EL1 and invoke the errata
+ * workaround directly since there is no return from exception when
+ * invoking the EFI run-time services.
+ */
+ uaccess_ttbr0_enable();
+ post_ttbr_update_workaround();
+
__efi_fpsimd_begin();
}

void arch_efi_call_virt_teardown(void)
{
__efi_fpsimd_end();
+
+ /*
+ * Defer the switch to the current thread's TTBR0_EL1 until
+ * uaccess_enable(). Do so before efi_virtmap_unload() updates the
+ * saved TTBR0 value, so the userland page tables are not activated
+ * inadvertently over the back of an exception.
+ */
+ uaccess_ttbr0_disable();
+
efi_virtmap_unload();
}

--
2.51.0.869.ge66316f041-goog