The start of the linear region map on a KASLR enabled ARM64 machine -
which supports a compatible EFI firmware (with EFI_RNG_PROTOCOL
support), is no longer correctly represented by the PAGE_OFFSET macro,
since it is defined as:
(UL(1) << (VA_BITS - 1)) + 1)
So taking an example of a platform with VA_BITS=48, this gives a static
value of:
PAGE_OFFSET = 0xffff800000000000
However, for the KASLR case, we use the 'memstart_offset_seed'
to randomize the linear region - since 'memstart_addr' indicates the
start of physical RAM, we randomize the same on basis
of 'memstart_offset_seed' value.
As the PAGE_OFFSET value is used presently by several user space
tools (for e.g. makedumpfile and crash tools) to determine the start
of linear region and hence to read addresses (like PT_NOTE fields) from
'/proc/kcore' for the non-KASLR boot cases, so it would be better to
use 'memblock_start_of_DRAM()' value (converted to virtual) as
the start of linear region for the KASLR cases and default to
the PAGE_OFFSET value for non-KASLR cases to indicate the start of
linear region.
I tested this on my qualcomm (which supports EFI_RNG_PROTOCOL)
and apm mustang (which does not support EFI_RNG_PROTOCOL) arm64 boards
and was able to use a modified user space utility (like kexec-tools and
makedumpfile) to determine the start of linear region correctly for
both the KASLR and non-KASLR boot cases.
Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Signed-off-by: Bhupesh Sharma <bhsharma@xxxxxxxxxx>
---
arch/arm64/include/asm/memory.h | 3 +++
arch/arm64/kernel/arm64ksyms.c | 1 +
arch/arm64/mm/init.c | 3 +++
3 files changed, 7 insertions(+)
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 49d99214f43c..bfd0915ecaf8 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -178,6 +178,9 @@ extern s64 memstart_addr;
/* PHYS_OFFSET - the physical address of the start of memory. */
#define PHYS_OFFSET ({ VM_BUG_ON(memstart_addr & 1); memstart_addr; })
+/* the virtual base of the linear region. */
+extern s64 linear_reg_start_addr;
+
/* the virtual base of the kernel image (minus TEXT_OFFSET) */
extern u64 kimage_vaddr;
diff --git a/arch/arm64/kernel/arm64ksyms.c b/arch/arm64/kernel/arm64ksyms.c
index d894a20b70b2..a92238ea45ff 100644
--- a/arch/arm64/kernel/arm64ksyms.c
+++ b/arch/arm64/kernel/arm64ksyms.c
@@ -42,6 +42,7 @@ EXPORT_SYMBOL(__arch_copy_in_user);
/* physical memory */
EXPORT_SYMBOL(memstart_addr);
+EXPORT_SYMBOL(linear_reg_start_addr);
/* string / mem functions */
EXPORT_SYMBOL(strchr);
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 325cfb3b858a..29447adb0eef 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -60,6 +60,7 @@
* that cannot be mistaken for a real physical address.
*/
s64 memstart_addr __ro_after_init = -1;
+s64 linear_reg_start_addr __ro_after_init = PAGE_OFFSET;
phys_addr_t arm64_dma_phys_limit __ro_after_init;
#ifdef CONFIG_BLK_DEV_INITRD
@@ -452,6 +453,8 @@ void __init arm64_memblock_init(void)
}
}
+ linear_reg_start_addr = __phys_to_virt(memblock_start_of_DRAM());
+
/*
* Register the kernel text, kernel data, initrd, and initial
* pagetables with memblock.
--
2.7.4
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