[PATCH v2] efi/arm: Disable LPAE PAN when calling EFI runtime services

[Ard Biesheuvel <ardb+git@google.com>]

From: Ard Biesheuvel <ardb@kernel.org>

EFI runtime services are remapped into the lower 1 GiB of virtual
address space at boot, so they are guaranteed to be able to co-exist
with the kernel virtual mappings without the need to allocate space for
them in the kernel's vmalloc region, which is rather small.

This means those mappings are covered by TTBR0 when LPAE PAN is enabled,
and so 'user' access must be enabled while such calls are in progress.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
In the end, I found a cleaner way to incorporate this into the existing
plumbing, without the need to rely on a global variable to stash the
TTBCR value.

 arch/arm/include/asm/efi.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm/include/asm/efi.h b/arch/arm/include/asm/efi.h
index 78282ced5038..e408399d5f0e 100644
--- a/arch/arm/include/asm/efi.h
+++ b/arch/arm/include/asm/efi.h
@@ -14,6 +14,7 @@
 #include <asm/mach/map.h>
 #include <asm/mmu_context.h>
 #include <asm/ptrace.h>
+#include <asm/uaccess.h>
 
 #ifdef CONFIG_EFI
 void efi_init(void);
@@ -25,6 +26,18 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md, boo
 #define arch_efi_call_virt_setup()	efi_virtmap_load()
 #define arch_efi_call_virt_teardown()	efi_virtmap_unload()
 
+#ifdef CONFIG_CPU_TTBR0_PAN
+#undef arch_efi_call_virt
+#define arch_efi_call_virt(p, f, args...) ({				\
+	unsigned int flags = uaccess_save_and_enable();			\
+	efi_status_t res = _Generic((p)->f(args),			\
+			efi_status_t:	(p)->f(args),			\
+			default:	((p)->f(args), EFI_ABORTED));	\
+	uaccess_restore(flags);						\
+	res;								\
+})
+#endif
+
 #define ARCH_EFI_IRQ_FLAGS_MASK \
 	(PSR_J_BIT | PSR_E_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT | \
 	 PSR_T_BIT | MODE_MASK)
-- 
2.45.2.505.gda0bf45e8d-goog