efi/libstub: arm: Print CPU boot mode and MMU state at boot

On 32-bit ARM, we may boot at HYP mode, or with the MMU and caches off
(or both), even though the EFI spec does not actually support this.
While booting at HYP mode is something we might tolerate, fiddling
with the caches is a more serious issue, as disabling the caches is
tricky to do safely from C code, and running without the Dcache makes
it impossible to support unaligned memory accesses, which is another
explicit requirement imposed by the EFI spec.

So take note of the CPU mode and MMU state in the EFI stub diagnostic
output so that we can easily diagnose any issues that may arise from
this. E.g.,

  EFI stub: Entering in SVC mode with MMU enabled

Also, capture the CPSR and SCTLR system register values at EFI stub
entry, and after ExitBootServices() returns, and check whether the
MMU and Dcache were disabled at any point. If this is the case, a
diagnostic message like the following will be emitted:

  efi: [Firmware Bug]: EFI stub was entered with MMU and Dcache disabled, please fix your firmware!
  efi: CPSR at EFI stub entry        : 0x600001d3
  efi: SCTLR at EFI stub entry       : 0x00c51838
  efi: CPSR after ExitBootServices() : 0x600001d3
  efi: SCTLR after ExitBootServices(): 0x00c50838

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>

4 files changed, 90 insertions, 3 deletions

diff --git a/drivers/firmware/efi/arm-init.c b/drivers/firmware/efi/arm-init.c
index 6f4baf70db16..71c445d20258 100644
--- a/drivers/firmware/efi/arm-init.c
+++ b/drivers/firmware/efi/arm-init.c
@@ -52,9 +52,11 @@ static phys_addr_t __init efi_to_phys(unsigned long addr)
 }
 
 static __initdata unsigned long screen_info_table = EFI_INVALID_TABLE_ADDR;
+static __initdata unsigned long cpu_state_table = EFI_INVALID_TABLE_ADDR;
 
 static const efi_config_table_type_t arch_tables[] __initconst = {
 	{LINUX_EFI_ARM_SCREEN_INFO_TABLE_GUID, &screen_info_table},
+	{LINUX_EFI_ARM_CPU_STATE_TABLE_GUID, &cpu_state_table},
 	{}
 };
 
@@ -240,9 +242,37 @@ void __init efi_init(void)
 
 	init_screen_info();
 
+#ifdef CONFIG_ARM
 	/* ARM does not permit early mappings to persist across paging_init() */
-	if (IS_ENABLED(CONFIG_ARM))
-		efi_memmap_unmap();
+	efi_memmap_unmap();
+
+	if (cpu_state_table != EFI_INVALID_TABLE_ADDR) {
+		struct efi_arm_entry_state *state;
+		bool dump_state = true;
+
+		state = early_memremap_ro(cpu_state_table,
+					  sizeof(struct efi_arm_entry_state));
+		if (state == NULL) {
+			pr_warn("Unable to map CPU entry state table.\n");
+			return;
+		}
+
+		if ((state->sctlr_before_ebs & 1) == 0)
+			pr_warn(FW_BUG "EFI stub was entered with MMU and Dcache disabled, please fix your firmware!\n");
+		else if ((state->sctlr_after_ebs & 1) == 0)
+			pr_warn(FW_BUG "ExitBootServices() returned with MMU and Dcache disabled, please fix your firmware!\n");
+		else
+			dump_state = false;
+
+		if (dump_state || efi_enabled(EFI_DBG)) {
+			pr_info("CPSR at EFI stub entry        : 0x%08x\n", state->cpsr_before_ebs);
+			pr_info("SCTLR at EFI stub entry       : 0x%08x\n", state->sctlr_before_ebs);
+			pr_info("CPSR after ExitBootServices() : 0x%08x\n", state->cpsr_after_ebs);
+			pr_info("SCTLR after ExitBootServices(): 0x%08x\n", state->sctlr_after_ebs);
+		}
+		early_memunmap(state, sizeof(struct efi_arm_entry_state));
+	}
+#endif
 }
 
 static bool efifb_overlaps_pci_range(const struct of_pci_range *range)
diff --git a/drivers/firmware/efi/libstub/arm32-stub.c b/drivers/firmware/efi/libstub/arm32-stub.c
index 40243f524556..d08e5d55838c 100644
--- a/drivers/firmware/efi/libstub/arm32-stub.c
+++ b/drivers/firmware/efi/libstub/arm32-stub.c
@@ -7,10 +7,49 @@
 
 #include "efistub.h"
 
+static efi_guid_t cpu_state_guid = LINUX_EFI_ARM_CPU_STATE_TABLE_GUID;
+
+struct efi_arm_entry_state *efi_entry_state;
+
+static void get_cpu_state(u32 *cpsr, u32 *sctlr)
+{
+	asm("mrs %0, cpsr" : "=r"(*cpsr));
+	if ((*cpsr & MODE_MASK) == HYP_MODE)
+		asm("mrc p15, 4, %0, c1, c0, 0" : "=r"(*sctlr));
+	else
+		asm("mrc p15, 0, %0, c1, c0, 0" : "=r"(*sctlr));
+}
+
 efi_status_t check_platform_features(void)
 {
+	efi_status_t status;
+	u32 cpsr, sctlr;
 	int block;
 
+	get_cpu_state(&cpsr, &sctlr);
+
+	efi_info("Entering in %s mode with MMU %sabled\n",
+		 ((cpsr & MODE_MASK) == HYP_MODE) ? "HYP" : "SVC",
+		 (sctlr & 1) ? "en" : "dis");
+
+	status = efi_bs_call(allocate_pool, EFI_LOADER_DATA,
+			     sizeof(*efi_entry_state),
+			     (void **)&efi_entry_state);
+	if (status != EFI_SUCCESS) {
+		efi_err("allocate_pool() failed\n");
+		return status;
+	}
+
+	efi_entry_state->cpsr_before_ebs = cpsr;
+	efi_entry_state->sctlr_before_ebs = sctlr;
+
+	status = efi_bs_call(install_configuration_table, &cpu_state_guid,
+			     efi_entry_state);
+	if (status != EFI_SUCCESS) {
+		efi_err("install_configuration_table() failed\n");
+		goto free_state;
+	}
+
 	/* non-LPAE kernels can run anywhere */
 	if (!IS_ENABLED(CONFIG_ARM_LPAE))
 		return EFI_SUCCESS;
@@ -19,9 +58,22 @@ efi_status_t check_platform_features(void)
 	block = cpuid_feature_extract(CPUID_EXT_MMFR0, 0);
 	if (block < 5) {
 		efi_err("This LPAE kernel is not supported by your CPU\n");
-		return EFI_UNSUPPORTED;
+		status = EFI_UNSUPPORTED;
+		goto drop_table;
 	}
 	return EFI_SUCCESS;
+
+drop_table:
+	efi_bs_call(install_configuration_table, &cpu_state_guid, NULL);
+free_state:
+	efi_bs_call(free_pool, efi_entry_state);
+	return status;
+}
+
+void efi_handle_post_ebs_state(void)
+{
+	get_cpu_state(&efi_entry_state->cpsr_after_ebs,
+		      &efi_entry_state->sctlr_after_ebs);
 }
 
 static efi_guid_t screen_info_guid = LINUX_EFI_ARM_SCREEN_INFO_TABLE_GUID;
diff --git a/drivers/firmware/efi/libstub/efi-stub.c b/drivers/firmware/efi/libstub/efi-stub.c
index e97370bdfdb0..3318ec3f8e5b 100644
--- a/drivers/firmware/efi/libstub/efi-stub.c
+++ b/drivers/firmware/efi/libstub/efi-stub.c
@@ -329,6 +329,9 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
 	if (status != EFI_SUCCESS)
 		goto fail_free_initrd;
 
+	if (IS_ENABLED(CONFIG_ARM))
+		efi_handle_post_ebs_state();
+
 	efi_enter_kernel(image_addr, fdt_addr, fdt_totalsize((void *)fdt_addr));
 	/* not reached */
 
diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index ac756f1fdb1a..2c9d42264c29 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -777,4 +777,6 @@ efi_status_t efi_load_initrd(efi_loaded_image_t *image,
 			     unsigned long soft_limit,
 			     unsigned long hard_limit);
 
+void efi_handle_post_ebs_state(void);
+
 #endif