[PATCH 0/3] UEFI stub pre-boot compat checks

As discussed earlier today [1], and last year [2], it makes sense for the
UEFI stub to perform some basic checks on the hardware for missing features
that would prevent the kernel from booting to a state where it can even
complain about this.

So implements this for ARM, to check on LPAE builds whether the CPU supports
it (patch #1), and for arm64, to check whether the build time granule is
implemented by the CPU (patch #2). Patch #3 wires it up into the shared init
code.

[1] http://thread.gmane.org/gmane.linux.ports.arm.kernel/472880
[2] http://thread.gmane.org/gmane.linux.ports.arm.kernel/447370

Ard Biesheuvel (3):
  ARM: efistub: check for LPAE support before booting a LPAE kernel
  arm64: efistub: check for h/w support before booting a >4 KB granule
    kernel
  ARM/arm64: efistub: perform hardware compatibility check

 drivers/firmware/efi/libstub/arm-stub.c   |  4 ++++
 drivers/firmware/efi/libstub/arm32-stub.c | 17 +++++++++++++++++
 drivers/firmware/efi/libstub/arm64-stub.c | 20 ++++++++++++++++++++
 drivers/firmware/efi/libstub/efistub.h    |  2 ++
 4 files changed, 43 insertions(+)

-- 
2.5.0

A kernel built with support for LPAE cannot boot to a state where it
can inform the user about it if it fails due to missing LPAE support
in the hardware.

If we happen to be booting via UEFI, we can fail gracefully so check
for LPAE support in the hardware on CONFIG_ARM_LPAE builds before
entering the kernel proper.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <redacted>
---
 drivers/firmware/efi/libstub/arm32-stub.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/firmware/efi/libstub/arm32-stub.c b/drivers/firmware/efi/libstub/arm32-stub.c
index 495ebd657e38..6f42be4d0084 100644
--- a/drivers/firmware/efi/libstub/arm32-stub.c
+++ b/drivers/firmware/efi/libstub/arm32-stub.c

@@ -9,6 +9,23 @@
 #include <linux/efi.h>
 #include <asm/efi.h>
 
+efi_status_t check_platform_features(efi_system_table_t *sys_table_arg)
+{
+	int block;
+
+	/* non-LPAE kernels can run anywhere */
+	if (!IS_ENABLED(CONFIG_ARM_LPAE))
+		return EFI_SUCCESS;
+
+	/* LPAE kernels need compatible hardware */
+	block = cpuid_feature_extract(CPUID_EXT_MMFR0, 0);
+	if (block < 5) {
+		pr_efi_err(sys_table_arg, "This LPAE kernel is not supported by your CPU\n");
+		return EFI_UNSUPPORTED;
+	}
+	return EFI_SUCCESS;
+}
+
 efi_status_t handle_kernel_image(efi_system_table_t *sys_table,
 				 unsigned long *image_addr,
 				 unsigned long *image_size,

-- 
2.5.0

A kernel built with support for a page size that is not supported by the
hardware it runs on cannot boot to a state where it can inform the user
about it.

If we happen to be booting via UEFI, we can fail gracefully so check
if the currently configured page size is supported by the hardware before
entering the kernel proper. Note that UEFI mandates support for 4 KB pages,
so in that case, no check is needed.

Suggested-by: Jeremy Linton <redacted>
Signed-off-by: Ard Biesheuvel <redacted>
---
 drivers/firmware/efi/libstub/arm64-stub.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c
index 9e0342745e4f..aef04ad60e0d 100644
--- a/drivers/firmware/efi/libstub/arm64-stub.c
+++ b/drivers/firmware/efi/libstub/arm64-stub.c

@@ -12,6 +12,26 @@
 #include <linux/efi.h>
 #include <asm/efi.h>
 #include <asm/sections.h>
+#include <asm/sysreg.h>
+
+efi_status_t check_platform_features(efi_system_table_t *sys_table_arg)
+{
+	u64 tg;
+
+	/* UEFI mandates support for 4 KB granule, no need to check */
+	if (IS_ENABLED(CONFIG_ARM64_4K_PAGES))
+		return EFI_SUCCESS;
+
+	tg = (read_cpuid(ID_AA64MMFR0_EL1) >> ID_AA64MMFR0_TGRAN_SHIFT) & 0xf;
+	if (tg != ID_AA64MMFR0_TGRAN_SUPPORTED) {
+		if (IS_ENABLED(CONFIG_ARM64_64K_PAGES))
+			pr_efi_err(sys_table_arg, "This 64 KB granule kernel is not supported by your CPU\n");
+		else
+			pr_efi_err(sys_table_arg, "This 16 KB granule kernel is not supported by your CPU\n");
+		return EFI_UNSUPPORTED;
+	}
+	return EFI_SUCCESS;
+}
 
 efi_status_t handle_kernel_image(efi_system_table_t *sys_table_arg,
 				 unsigned long *image_addr,

-- 
2.5.0

Before proceeding with relocating the kernel and parsing the command line,
insert a call to check_platform_features() to allow an arch specific check
to be performed whether the current kernel can execute on the current
hardware.

Signed-off-by: Ard Biesheuvel <redacted>
---
 drivers/firmware/efi/libstub/arm-stub.c | 4 ++++
 drivers/firmware/efi/libstub/efistub.h  | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index 3397902e4040..6086a874fa3c 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c

@@ -190,6 +190,10 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
 
 	pr_efi(sys_table, "Booting Linux Kernel...\n");
 
+	status = check_platform_features(sys_table);
+	if (status != EFI_SUCCESS)
+		goto fail;
+
 	/*
 	 * Get a handle to the loaded image protocol.  This is used to get
 	 * information about the running image, such as size and the command

diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index 6b6548fda089..33b1284c7319 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h

@@ -43,4 +43,6 @@ void efi_get_virtmap(efi_memory_desc_t *memory_map, unsigned long map_size,
 		     unsigned long desc_size, efi_memory_desc_t *runtime_map,
 		     int *count);
 
+efi_status_t check_platform_features(efi_system_table_t *sys_table_arg);
+
 #endif

-- 
2.5.0

On 28/01/16 17:02, Ard Biesheuvel wrote:

As discussed earlier today [1], and last year [2], it makes sense for the
UEFI stub to perform some basic checks on the hardware for missing features
that would prevent the kernel from booting to a state where it can even
complain about this.

So implements this for ARM, to check on LPAE builds whether the CPU supports
it (patch #1), and for arm64, to check whether the build time granule is
implemented by the CPU (patch #2). Patch #3 wires it up into the shared init
code.

[1] http://thread.gmane.org/gmane.linux.ports.arm.kernel/472880
[2] http://thread.gmane.org/gmane.linux.ports.arm.kernel/447370

Ard,

Thanks for the quick solution. I tested this on Juno for 16K granule.
So, for arm64:

Tested-by: Suzuki K Poulose <suzuki.poulose@arm.com>


Cheers
Suzuki

On 01/28/2016 11:02 AM, Ard Biesheuvel wrote:

As discussed earlier today [1], and last year [2], it makes sense for the
UEFI stub to perform some basic checks on the hardware for missing features
that would prevent the kernel from booting to a state where it can even
complain about this.

So implements this for ARM, to check on LPAE builds whether the CPU supports
it (patch #1), and for arm64, to check whether the build time granule is
implemented by the CPU (patch #2). Patch #3 wires it up into the shared init
code.

Ard,

This version looks good, and addresses all the reservations from the 16k 
page thread. Thanks!

Reviewed-by: Jeremy Linton <redacted>