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>

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