Commit 68d23da4 authored by Will Deacon's avatar Will Deacon
Browse files

arm64: Kconfig: Re-jig CONFIG options for 52-bit VA 



Enabling 52-bit VAs for userspace is pretty confusing, since it requires
you to select "48-bit" virtual addressing in the Kconfig.

Rework the logic so that 52-bit user virtual addressing is advertised in
the "Virtual address space size" choice, along with some help text to
describe its interaction with Pointer Authentication. The EXPERT-only
option to force all user mappings to the 52-bit range is then made
available immediately below the VA size selection.

Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent b9567720

arch/arm64/Kconfig

+29 −18
Original line number Diff line number Diff line
@@ -682,15 +682,43 @@ config ARM64_VA_BITS_47 
config ARM64_VA_BITS_48

	bool "48-bit"



config ARM64_USER_VA_BITS_52

	bool "52-bit (user)"

	depends on ARM64_64K_PAGES && (ARM64_PAN || !ARM64_SW_TTBR0_PAN)

	help

	  Enable 52-bit virtual addressing for userspace when explicitly

	  requested via a hint to mmap(). The kernel will continue to

	  use 48-bit virtual addresses for its own mappings.



	  NOTE: Enabling 52-bit virtual addressing in conjunction with

	  ARMv8.3 Pointer Authentication will result in the PAC being

	  reduced from 7 bits to 3 bits, which may have a significant

	  impact on its susceptibility to brute-force attacks.



	  If unsure, select 48-bit virtual addressing instead.



endchoice



config ARM64_FORCE_52BIT

	bool "Force 52-bit virtual addresses for userspace"

	depends on ARM64_USER_VA_BITS_52 && EXPERT

	help

	  For systems with 52-bit userspace VAs enabled, the kernel will attempt

	  to maintain compatibility with older software by providing 48-bit VAs

	  unless a hint is supplied to mmap.



	  This configuration option disables the 48-bit compatibility logic, and

	  forces all userspace addresses to be 52-bit on HW that supports it. One

	  should only enable this configuration option for stress testing userspace

	  memory management code. If unsure say N here.



config ARM64_VA_BITS

	int

	default 36 if ARM64_VA_BITS_36

	default 39 if ARM64_VA_BITS_39

	default 42 if ARM64_VA_BITS_42

	default 47 if ARM64_VA_BITS_47

	default 48 if ARM64_VA_BITS_48

	default 48 if ARM64_VA_BITS_48 || ARM64_USER_VA_BITS_52



choice

	prompt "Physical address space size"
@@ -716,10 +744,6 @@ config ARM64_PA_BITS_52 


endchoice



config ARM64_52BIT_VA

	def_bool y

	depends on ARM64_VA_BITS_48 && ARM64_64K_PAGES && (ARM64_PAN || !ARM64_SW_TTBR0_PAN)



config ARM64_PA_BITS

	int

	default 48 if ARM64_PA_BITS_48
@@ -1186,19 +1210,6 @@ config ARM64_CNP 
	  at runtime, and does not affect PEs that do not implement

	  this feature.



config ARM64_FORCE_52BIT

	bool "Force 52-bit virtual addresses for userspace"

	depends on ARM64_52BIT_VA && EXPERT

	help

	  For systems with 52-bit userspace VAs enabled, the kernel will attempt

	  to maintain compatibility with older software by providing 48-bit VAs

	  unless a hint is supplied to mmap.



	  This configuration option disables the 48-bit compatibility logic, and

	  forces all userspace addresses to be 52-bit on HW that supports it. One

	  should only enable this configuration option for stress testing userspace

	  memory management code. If unsure say N here.



endmenu



config ARM64_SVE

arch/arm64/include/asm/assembler.h

+2 −2
Original line number Diff line number Diff line
@@ -549,7 +549,7 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU 
 * 	ttbr: Value of ttbr to set, modified.

 */

	.macro	offset_ttbr1, ttbr

#ifdef CONFIG_ARM64_52BIT_VA

#ifdef CONFIG_ARM64_USER_VA_BITS_52

	orr	\ttbr, \ttbr, #TTBR1_BADDR_4852_OFFSET

#endif

	.endm
@@ -560,7 +560,7 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU 
 * to be nop'ed out when dealing with 52-bit kernel VAs.

 */

	.macro	restore_ttbr1, ttbr

#ifdef CONFIG_ARM64_52BIT_VA

#ifdef CONFIG_ARM64_USER_VA_BITS_52

	bic	\ttbr, \ttbr, #TTBR1_BADDR_4852_OFFSET

#endif

	.endm

arch/arm64/include/asm/mmu_context.h

+1 −1
Original line number Diff line number Diff line
@@ -74,7 +74,7 @@ extern u64 idmap_ptrs_per_pgd; 


static inline bool __cpu_uses_extended_idmap(void)

{

	if (IS_ENABLED(CONFIG_ARM64_52BIT_VA))

	if (IS_ENABLED(CONFIG_ARM64_USER_VA_BITS_52))

		return false;



	return unlikely(idmap_t0sz != TCR_T0SZ(VA_BITS));

arch/arm64/include/asm/pgtable-hwdef.h

+2 −2
Original line number Diff line number Diff line
@@ -80,7 +80,7 @@ 
#define PGDIR_SHIFT		ARM64_HW_PGTABLE_LEVEL_SHIFT(4 - CONFIG_PGTABLE_LEVELS)

#define PGDIR_SIZE		(_AC(1, UL) << PGDIR_SHIFT)

#define PGDIR_MASK		(~(PGDIR_SIZE-1))

#ifdef CONFIG_ARM64_52BIT_VA

#ifdef CONFIG_ARM64_USER_VA_BITS_52

#define PTRS_PER_PGD		(1 << (52 - PGDIR_SHIFT))

#else

#define PTRS_PER_PGD		(1 << (VA_BITS - PGDIR_SHIFT))
@@ -310,7 +310,7 @@ 
#define TTBR_BADDR_MASK_52	(((UL(1) << 46) - 1) << 2)

#endif



#ifdef CONFIG_ARM64_52BIT_VA

#ifdef CONFIG_ARM64_USER_VA_BITS_52

/* Must be at least 64-byte aligned to prevent corruption of the TTBR */

#define TTBR1_BADDR_4852_OFFSET	(((UL(1) << (52 - PGDIR_SHIFT)) - \

				 (UL(1) << (48 - PGDIR_SHIFT))) * 8)

arch/arm64/include/asm/processor.h

+2 −2
Original line number Diff line number Diff line
@@ -20,11 +20,11 @@ 
#define __ASM_PROCESSOR_H



#define KERNEL_DS		UL(-1)

#ifdef CONFIG_ARM64_52BIT_VA

#ifdef CONFIG_ARM64_USER_VA_BITS_52

#define USER_DS			((UL(1) << 52) - 1)

#else

#define USER_DS			((UL(1) << VA_BITS) - 1)

#endif /* CONFIG_ARM64_52BIT_VA */

#endif /* CONFIG_ARM64_USER_VA_BITS_52 */



/*

 * On arm64 systems, unaligned accesses by the CPU are cheap, and so there is

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