[devel] [PATCH 22/35] arm64-stub: fixed secondary cores boot on Baikal-M SoC

[asheplyakov на yandex.ru]

From: Alexey Sheplyakov <asheplyakov на altlinux.org>

Old versions of Baikal-M firmware (ARM-TF) deny execution attempts
outside of the (physical) address ranges
[0x80000000, 0x8FFFFFFF] and [0xA0000000, 0xBFFFFFFF]
Thus PSCI calls to boot secondary cores fail unless the kernel image
resides in one of these address ranges. However UEFI PE/COFF loader
puts the kernel image into the forbidden range. Since the alignment
is good enough EFI stub does not try to relocate the kernel.
As a result secondary CPUs fail to boot.

Relocation to a random address is not going to work either.
Therefore automatically disable kaslr on "known bad" systems (for
now only Baikal-M) and forcibly relocate the kernel to a low(er)
address.

This patch is necessary only for old firmware (pre SDK-M 5.1) and
prevents kalsr from working on Baikal-M systems.

X-DONTUPSTREAM
X-legacy
X-feature-Baikal-M
---
 drivers/firmware/efi/libstub/arm64-stub.c | 62 ++++++++++++++++++++++-
 1 file changed, 61 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c
index 9cc556013d08..5486a223a59f 100644
--- a/drivers/firmware/efi/libstub/arm64-stub.c
+++ b/drivers/firmware/efi/libstub/arm64-stub.c
@@ -11,6 +11,7 @@
 #include <asm/efi.h>
 #include <asm/memory.h>
 #include <asm/sections.h>
+#include <linux/libfdt.h>
 #include <asm/sysreg.h>
 
 #include "efistub.h"
@@ -34,6 +35,31 @@ efi_status_t check_platform_features(void)
 	return EFI_SUCCESS;
 }
 
+static const char* machines_need_low_alloc[] = {
+	"baikal,baikal-m",
+};
+
+static bool need_low_alloc(void) {
+	size_t i;
+	const void *fdt;
+	const char *match;
+
+	fdt = get_efi_config_table(DEVICE_TREE_GUID);
+	if (!fdt) {
+		efi_info("failed to retrive FDT from EFI\n");
+		return false;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(machines_need_low_alloc); i++) {
+		match = machines_need_low_alloc[i];
+		if (fdt_node_check_compatible(fdt, 0, match) == 0) {
+			efi_info("machine %s: forcing kernel relocation to low address\n", match);
+			return true;
+		}
+	}
+	return false;
+}
+
 /*
  * Distro versions of GRUB may ignore the BSS allocation entirely (i.e., fail
  * to provide space, and fail to zero it). Check for this condition by double
@@ -79,6 +105,19 @@ static bool check_image_region(u64 base, u64 size)
 	return ret;
 }
 
+static inline efi_status_t efi_low_alloc(unsigned long size, unsigned long align,
+					 unsigned long *addr)
+{
+	/*
+	 * Don't allocate at 0x0. It will confuse code that
+	 * checks pointers against NULL. Skip the first 8
+	 * bytes so we start at a nice even number.
+	 */
+	return efi_low_alloc_above(size, align, addr, 0x8);
+}
+
+
+
 efi_status_t handle_kernel_image(unsigned long *image_addr,
 				 unsigned long *image_size,
 				 unsigned long *reserve_addr,
@@ -99,6 +138,14 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 	 */
 	u64 min_kimg_align = efi_nokaslr ? MIN_KIMG_ALIGN : EFI_KIMG_ALIGN;
 
+	bool force_low_reloc = need_low_alloc();
+	if (force_low_reloc) {
+		if (!efi_nokaslr) {
+			efi_info("booting on a broken firmware, KASLR will be disabled\n");
+			efi_nokaslr = true;
+		}
+	}
+
 	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
 		if (!efi_nokaslr) {
 			status = efi_get_random_bytes(sizeof(phys_seed),
@@ -112,7 +159,8 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 				efi_nokaslr = true;
 			}
 		} else {
-			efi_info("KASLR disabled on kernel command line\n");
+			if (!force_low_reloc)
+				efi_info("KASLR disabled on kernel command line\n");
 		}
 	}
 
@@ -140,6 +188,15 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 		status = EFI_OUT_OF_RESOURCES;
 	}
 
+	if (force_low_reloc) {
+		status = efi_low_alloc(*reserve_size,
+				       min_kimg_align,
+				       reserve_addr);
+		if (status != EFI_SUCCESS) {
+			efi_err("Failed to relocate kernel, expect secondary CPUs boot failure\n");
+		}
+	}
+
 	if (status != EFI_SUCCESS) {
 		if (!check_image_region((u64)_text, kernel_memsize)) {
 			efi_err("FIRMWARE BUG: Image BSS overlaps adjacent EFI memory region\n");
@@ -164,6 +221,9 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 	}
 
 	*image_addr = *reserve_addr;
+	if (efi_nokaslr) {
+		efi_info("relocating kernel to 0x%lx\n", *image_addr);
+	}
 	memcpy((void *)*image_addr, _text, kernel_size);
 
 	return EFI_SUCCESS;
-- 
2.32.0