x86/efi: Clean up efi CR3 save/restore

efi_call_phys_prolog() used to return a "pgd_t *" that meant one of
three different things depending on kernel and system configuration.
Clean it up so it uses a union and is more explicit about what's
going on.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>

4 files changed, 36 insertions, 21 deletions

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 2f77bcefe6b494..6d74cc3802e631 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -111,11 +111,24 @@ extern void __iomem *__init efi_ioremap(unsigned long addr, unsigned long size,
 
 #endif /* CONFIG_X86_32 */
 
+union efi_saved_pgd {
+	/*
+	 * If !EFI_OLD_MEMMAP or we're 32-bit, this is a verbatim saved CR3
+	 * value.
+	 */
+	unsigned long cr3;
+
+#ifdef CONFIG_X86_64
+	/* If EFI_OLD_MEMMAP, this is a kmalloced copy of the pgd. */
+	pgd_t *pgd;
+#endif
+};
+
 extern struct efi_scratch efi_scratch;
 extern void __init efi_set_executable(efi_memory_desc_t *md, bool executable);
 extern int __init efi_memblock_x86_reserve_range(void);
-extern pgd_t * __init efi_call_phys_prolog(void);
-extern void __init efi_call_phys_epilog(pgd_t *save_pgd);
+extern union efi_saved_pgd __init efi_call_phys_prolog(void);
+extern void __init efi_call_phys_epilog(union efi_saved_pgd saved_pgd);
 extern void __init efi_print_memmap(void);
 extern void __init efi_memory_uc(u64 addr, unsigned long size);
 extern void __init efi_map_region(efi_memory_desc_t *md);
diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 565dff3c9a12cf..217dc166c64977 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -81,9 +81,9 @@ static efi_status_t __init phys_efi_set_virtual_address_map(
 {
 	efi_status_t status;
 	unsigned long flags;
-	pgd_t *save_pgd;
+	union efi_saved_pgd saved_pgd;
 
-	save_pgd = efi_call_phys_prolog();
+	saved_pgd = efi_call_phys_prolog();
 
 	/* Disable interrupts around EFI calls: */
 	local_irq_save(flags);
@@ -92,7 +92,7 @@ static efi_status_t __init phys_efi_set_virtual_address_map(
 			       descriptor_version, virtual_map);
 	local_irq_restore(flags);
 
-	efi_call_phys_epilog(save_pgd);
+	efi_call_phys_epilog(saved_pgd);
 
 	return status;
 }
diff --git a/arch/x86/platform/efi/efi_32.c b/arch/x86/platform/efi/efi_32.c
index cef39b0976498c..9b1abcf6e7bbf3 100644
--- a/arch/x86/platform/efi/efi_32.c
+++ b/arch/x86/platform/efi/efi_32.c
@@ -58,13 +58,13 @@ void __init efi_map_region(efi_memory_desc_t *md)
 void __init efi_map_region_fixed(efi_memory_desc_t *md) {}
 void __init parse_efi_setup(u64 phys_addr, u32 data_len) {}
 
-pgd_t * __init efi_call_phys_prolog(void)
+union efi_saved_pgd __init efi_call_phys_prolog(void)
 {
 	struct desc_ptr gdt_descr;
-	pgd_t *save_pgd;
+	union efi_saved_pgd saved_pgd;
 
 	/* Current pgd is swapper_pg_dir, we'll restore it later: */
-	save_pgd = swapper_pg_dir;
+	saved_pgd.cr3 = __pa(swapper_pg_dir);
 	load_cr3(initial_page_table);
 	__flush_tlb_all();
 
@@ -72,10 +72,10 @@ pgd_t * __init efi_call_phys_prolog(void)
 	gdt_descr.size = GDT_SIZE - 1;
 	load_gdt(&gdt_descr);
 
-	return save_pgd;
+	return saved_pgd;
 }
 
-void __init efi_call_phys_epilog(pgd_t *save_pgd)
+void __init efi_call_phys_epilog(union efi_saved_pgd saved_pgd)
 {
 	struct desc_ptr gdt_descr;
 
@@ -83,7 +83,7 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
 	gdt_descr.size = GDT_SIZE - 1;
 	load_gdt(&gdt_descr);
 
-	load_cr3(save_pgd);
+	write_cr3(saved_pgd.cr3);
 	__flush_tlb_all();
 }
 
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index ee966aaf51b2e5..de9652bd19d40c 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -69,16 +69,16 @@ static void __init early_code_mapping_set_exec(int executable)
 	}
 }
 
-pgd_t * __init efi_call_phys_prolog(void)
+union efi_saved_pgd __init efi_call_phys_prolog(void)
 {
 	unsigned long vaddress;
-	pgd_t *save_pgd;
+	union efi_saved_pgd saved_pgd;
 
 	int pgd;
 	int n_pgds;
 
 	if (!efi_enabled(EFI_OLD_MEMMAP)) {
-		save_pgd = (pgd_t *)read_cr3();
+		saved_pgd.cr3 = read_cr3();
 		write_cr3((unsigned long)efi_scratch.efi_pgt);
 		goto out;
 	}
@@ -86,20 +86,21 @@ pgd_t * __init efi_call_phys_prolog(void)
 	early_code_mapping_set_exec(1);
 
 	n_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT), PGDIR_SIZE);
-	save_pgd = kmalloc_array(n_pgds, sizeof(*save_pgd), GFP_KERNEL);
+	saved_pgd.pgd = kmalloc_array(n_pgds, sizeof(*saved_pgd.pgd),
+				      GFP_KERNEL);
 
 	for (pgd = 0; pgd < n_pgds; pgd++) {
-		save_pgd[pgd] = *pgd_offset_k(pgd * PGDIR_SIZE);
+		saved_pgd.pgd[pgd] = *pgd_offset_k(pgd * PGDIR_SIZE);
 		vaddress = (unsigned long)__va(pgd * PGDIR_SIZE);
 		set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), *pgd_offset_k(vaddress));
 	}
 out:
 	__flush_tlb_all();
 
-	return save_pgd;
+	return saved_pgd;
 }
 
-void __init efi_call_phys_epilog(pgd_t *save_pgd)
+void __init efi_call_phys_epilog(union efi_saved_pgd saved_pgd)
 {
 	/*
 	 * After the lock is released, the original page table is restored.
@@ -108,7 +109,7 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
 	int nr_pgds;
 
 	if (!efi_enabled(EFI_OLD_MEMMAP)) {
-		write_cr3((unsigned long)save_pgd);
+		write_cr3(saved_pgd.cr3);
 		__flush_tlb_all();
 		return;
 	}
@@ -116,9 +117,10 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
 	nr_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT) , PGDIR_SIZE);
 
 	for (pgd_idx = 0; pgd_idx < nr_pgds; pgd_idx++)
-		set_pgd(pgd_offset_k(pgd_idx * PGDIR_SIZE), save_pgd[pgd_idx]);
+		set_pgd(pgd_offset_k(pgd_idx * PGDIR_SIZE),
+			saved_pgd.pgd[pgd_idx]);
 
-	kfree(save_pgd);
+	kfree(saved_pgd.pgd);
 
 	__flush_tlb_all();
 	early_code_mapping_set_exec(0);