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authorWill Deacon <will.deacon@arm.com>2018-12-10 14:15:15 +0000
committerWill Deacon <will.deacon@arm.com>2018-12-10 18:42:18 +0000
commit68d23da4373aba76f5300017c4746440f276698e (patch)
tree138b93b628cf77727970417690693f18eddf7c40 /arch/arm64/Kconfig
parentarm64: mm: Allow forcing all userspace addresses to 52-bit (diff)
downloadlinux-dev-68d23da4373aba76f5300017c4746440f276698e.tar.xz
linux-dev-68d23da4373aba76f5300017c4746440f276698e.zip
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: Will Deacon <will.deacon@arm.com>
Diffstat (limited to '')
-rw-r--r--arch/arm64/Kconfig47
1 files changed, 29 insertions, 18 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index ca1f93233b22..905ce1653e82 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -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