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Commit 90ec95cd authored by Steve Capper's avatar Steve Capper Committed by Will Deacon
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arm64: mm: Introduce VA_BITS_MIN 



In order to support 52-bit kernel addresses detectable at boot time, the
kernel needs to know the most conservative VA_BITS possible should it
need to fall back to this quantity due to lack of hardware support.

A new compile time constant VA_BITS_MIN is introduced in this patch and
it is employed in the KASAN end address, KASLR, and EFI stub.

For Arm, if 52-bit VA support is unavailable the fallback is to 48-bits.

In other words: VA_BITS_MIN = min (48, VA_BITS)

Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarSteve Capper <steve.capper@arm.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 99426e5e

arch/arm64/include/asm/efi.h

+2 −2
Original line number Diff line number Diff line
@@ -79,7 +79,7 @@ static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base) 


/*

 * On arm64, we have to ensure that the initrd ends up in the linear region,

 * which is a 1 GB aligned region of size '1UL << (VA_BITS - 1)' that is

 * which is a 1 GB aligned region of size '1UL << (VA_BITS_MIN - 1)' that is

 * guaranteed to cover the kernel Image.

 *

 * Since the EFI stub is part of the kernel Image, we can relax the
@@ -90,7 +90,7 @@ static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base) 
static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,

						    unsigned long image_addr)

{

	return (image_addr & ~(SZ_1G - 1UL)) + (1UL << (VA_BITS - 1));

	return (image_addr & ~(SZ_1G - 1UL)) + (1UL << (VA_BITS_MIN - 1));

}



#define efi_call_early(f, ...)		sys_table_arg->boottime->f(__VA_ARGS__)

arch/arm64/include/asm/memory.h

+8 −1
Original line number Diff line number Diff line
@@ -52,6 +52,13 @@ 
#define PCI_IO_END		(VMEMMAP_START - SZ_2M)

#define PCI_IO_START		(PCI_IO_END - PCI_IO_SIZE)

#define FIXADDR_TOP		(PCI_IO_START - SZ_2M)

#if VA_BITS > 48

#define VA_BITS_MIN		(48)

#else

#define VA_BITS_MIN		(VA_BITS)

#endif

#define _VA_START(va)		(UL(0xffffffffffffffff) - \

				(UL(1) << ((va) - 1)) + 1)



#define KERNEL_START      _text

#define KERNEL_END        _end
@@ -74,7 +81,7 @@ 
#define KASAN_THREAD_SHIFT	1

#else

#define KASAN_THREAD_SHIFT	0

#define KASAN_SHADOW_END	(VA_START)

#define KASAN_SHADOW_END	(_VA_START(VA_BITS_MIN))

#endif



#define MIN_THREAD_SHIFT	(14 + KASAN_THREAD_SHIFT)

arch/arm64/include/asm/processor.h

+1 −1
Original line number Diff line number Diff line
@@ -42,7 +42,7 @@ 
 * TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area.

 */



#define DEFAULT_MAP_WINDOW_64	(UL(1) << VA_BITS)

#define DEFAULT_MAP_WINDOW_64	(UL(1) << VA_BITS_MIN)

#define TASK_SIZE_64		(UL(1) << vabits_user)



#ifdef CONFIG_COMPAT

arch/arm64/kernel/head.S

+1 −1
Original line number Diff line number Diff line
@@ -314,7 +314,7 @@ __create_page_tables: 
	mov	x5, #52

	cbnz	x6, 1f

#endif

	mov	x5, #VA_BITS

	mov	x5, #VA_BITS_MIN

1:

	adr_l	x6, vabits_user

	str	x5, [x6]

arch/arm64/kernel/kaslr.c

+3 −3
Original line number Diff line number Diff line
@@ -116,15 +116,15 @@ u64 __init kaslr_early_init(u64 dt_phys) 
	/*

	 * OK, so we are proceeding with KASLR enabled. Calculate a suitable

	 * kernel image offset from the seed. Let's place the kernel in the

	 * middle half of the VMALLOC area (VA_BITS - 2), and stay clear of

	 * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of

	 * the lower and upper quarters to avoid colliding with other

	 * allocations.

	 * Even if we could randomize at page granularity for 16k and 64k pages,

	 * let's always round to 2 MB so we don't interfere with the ability to

	 * map using contiguous PTEs

	 */

	mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1);

	offset = BIT(VA_BITS - 3) + (seed & mask);

	mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1);

	offset = BIT(VA_BITS_MIN - 3) + (seed & mask);



	/* use the top 16 bits to randomize the linear region */

	memstart_offset_seed = seed >> 48;