[PATCH v2 2/3] efi: arm64: Wire up BTI annotation in memory attributes table

[Ard Biesheuvel <ardb@xxxxxxxxxx>]

UEFI v2.10 extends the EFI memory attributes table with a flag that
indicates whether or not all RuntimeServicesCode regions were
constructed with BTI landing pads, permitting the OS to map these
regions with BTI restrictions enabled.

So let's take this into account on arm64.

Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 arch/arm64/kernel/efi.c   | 14 ++++++++++++--
 arch/arm64/kernel/traps.c |  6 ++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index 78ffd5aaddcbbaee..99971cd349f36310 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -96,15 +96,23 @@ int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md)
 	return 0;
 }
 
+struct set_perm_data {
+	const efi_memory_desc_t	*md;
+	bool			has_bti;
+};
+
 static int __init set_permissions(pte_t *ptep, unsigned long addr, void *data)
 {
-	efi_memory_desc_t *md = data;
+	struct set_perm_data *spd = data;
+	const efi_memory_desc_t *md = spd->md;
 	pte_t pte = READ_ONCE(*ptep);
 
 	if (md->attribute & EFI_MEMORY_RO)
 		pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
 	if (md->attribute & EFI_MEMORY_XP)
 		pte = set_pte_bit(pte, __pgprot(PTE_PXN));
+	else if (system_supports_bti() && spd->has_bti)
+		pte = set_pte_bit(pte, __pgprot(PTE_GP));
 	set_pte(ptep, pte);
 	return 0;
 }
@@ -113,6 +121,8 @@ int __init efi_set_mapping_permissions(struct mm_struct *mm,
 				       efi_memory_desc_t *md,
 				       bool has_bti)
 {
+	struct set_perm_data data = { md, has_bti };
+
 	BUG_ON(md->type != EFI_RUNTIME_SERVICES_CODE &&
 	       md->type != EFI_RUNTIME_SERVICES_DATA);
 
@@ -128,7 +138,7 @@ int __init efi_set_mapping_permissions(struct mm_struct *mm,
 	 */
 	return apply_to_page_range(mm, md->virt_addr,
 				   md->num_pages << EFI_PAGE_SHIFT,
-				   set_permissions, md);
+				   set_permissions, &data);
 }
 
 /*
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 4c0caa589e12de2a..1f366b94ea8e233a 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -18,6 +18,7 @@
 #include <linux/module.h>
 #include <linux/kexec.h>
 #include <linux/delay.h>
+#include <linux/efi.h>
 #include <linux/init.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/debug.h>
@@ -33,6 +34,7 @@
 #include <asm/cpufeature.h>
 #include <asm/daifflags.h>
 #include <asm/debug-monitors.h>
+#include <asm/efi.h>
 #include <asm/esr.h>
 #include <asm/exception.h>
 #include <asm/extable.h>
@@ -492,6 +494,10 @@ void do_el0_bti(struct pt_regs *regs)
 
 void do_el1_bti(struct pt_regs *regs, unsigned long esr)
 {
+	if (efi_runtime_fixup_exception(regs, "BTI violation")) {
+		regs->pstate &= ~PSR_BTYPE_MASK;
+		return;
+	}
 	die("Oops - BTI", regs, esr);
 }
 
-- 
2.39.1