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arm64: relocatable: deal with physically misaligned kernel images 

When booting a relocatable kernel image, there is no practical reason
to refuse an image whose load address is not exactly TEXT_OFFSET bytes
above a 2 MB aligned base address, as long as the physical and virtual
misalignment with respect to the swapper block size are equal, and are
both aligned to THREAD_SIZE.

Since the virtual misalignment is under our control when we first enter
the kernel proper, we can simply choose its value to be equal to the
physical misalignment.

So treat the misalignment of the physical load address as the initial
KASLR offset, and fix up the remaining code to deal with that.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Ard Biesheuvel 2016-04-18 17:09:47 +02:00 committed by Will Deacon
parent 18b9c0d641
commit 08cdac619c
2 changed files with 9 additions and 6 deletions
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9
arch/arm64/kernel/head.S
View File

@ -25,6 +25,7 @@
#include <linux/irqchip/arm-gic-v3.h>
#include <asm/assembler.h>
#include <asm/boot.h>
#include <asm/ptrace.h>
#include <asm/asm-offsets.h>
#include <asm/cache.h>
@ -213,8 +214,8 @@ efi_header_end:
ENTRY(stext)
bl preserve_boot_args
bl el2_setup // Drop to EL1, w20=cpu_boot_mode
mov x23, xzr // KASLR offset, defaults to 0
adrp x24, __PHYS_OFFSET
and x23, x24, MIN_KIMG_ALIGN - 1 // KASLR offset, defaults to 0
bl set_cpu_boot_mode_flag
bl __create_page_tables // x25=TTBR0, x26=TTBR1
/*
@ -449,11 +450,13 @@ __primary_switched:
bl kasan_early_init
#endif
#ifdef CONFIG_RANDOMIZE_BASE
cbnz x23, 0f // already running randomized?
tst x23, ~(MIN_KIMG_ALIGN - 1) // already running randomized?
b.ne 0f
mov x0, x21 // pass FDT address in x0
mov x1, x23 // pass modulo offset in x1
bl kaslr_early_init // parse FDT for KASLR options
cbz x0, 0f // KASLR disabled? just proceed
mov x23, x0 // record KASLR offset
orr x23, x23, x0 // record KASLR offset
ret x28 // we must enable KASLR, return
// to __enable_mmu()
0:

6
arch/arm64/kernel/kaslr.c
View File

@ -74,7 +74,7 @@ extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size,
* containing function pointers) to be reinitialized, and zero-initialized
* .bss variables will be reset to 0.
*/
u64 __init kaslr_early_init(u64 dt_phys)
u64 __init kaslr_early_init(u64 dt_phys, u64 modulo_offset)
{
void *fdt;
u64 seed, offset, mask, module_range;
@ -132,8 +132,8 @@ u64 __init kaslr_early_init(u64 dt_phys)
* boundary (for 4KB/16KB/64KB granule kernels, respectively). If this
* happens, increase the KASLR offset by the size of the kernel image.
*/
if ((((u64)_text + offset) >> SWAPPER_TABLE_SHIFT) !=
(((u64)_end + offset) >> SWAPPER_TABLE_SHIFT))
if ((((u64)_text + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT) !=
(((u64)_end + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT))
offset = (offset + (u64)(_end - _text)) & mask;
if (IS_ENABLED(CONFIG_KASAN))