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authorJames Morse <james.morse@arm.com>2016-02-05 14:58:48 +0000
committerCatalin Marinas <catalin.marinas@arm.com>2016-02-18 17:27:04 +0000
commit57f4959bad0a154aeca125b7d38d1d9471a12422 (patch)
tree6d75f86840bb0bd2d3f4928993f696c44e2033c0 /arch/arm64/Kconfig
parentarm64: add ARMv8.2 id_aa64mmfr2 boiler plate (diff)
downloadlinux-dev-57f4959bad0a154aeca125b7d38d1d9471a12422.tar.xz
linux-dev-57f4959bad0a154aeca125b7d38d1d9471a12422.zip
arm64: kernel: Add support for User Access Override
'User Access Override' is a new ARMv8.2 feature which allows the unprivileged load and store instructions to be overridden to behave in the normal way. This patch converts {get,put}_user() and friends to use ldtr*/sttr* instructions - so that they can only access EL0 memory, then enables UAO when fs==KERNEL_DS so that these functions can access kernel memory. This allows user space's read/write permissions to be checked against the page tables, instead of testing addr<USER_DS, then using the kernel's read/write permissions. Signed-off-by: James Morse <james.morse@arm.com> [catalin.marinas@arm.com: move uao_thread_switch() above dsb()] Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to '')
-rw-r--r--arch/arm64/Kconfig21
1 files changed, 21 insertions, 0 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index fa51ff0470c1..3d9cab156740 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -756,6 +756,27 @@ config ARM64_LSE_ATOMICS
endmenu
+config ARM64_UAO
+ bool "Enable support for User Access Override (UAO)"
+ default y
+ help
+ User Access Override (UAO; part of the ARMv8.2 Extensions)
+ causes the 'unprivileged' variant of the load/store instructions to
+ be overriden to be privileged.
+
+ This option changes get_user() and friends to use the 'unprivileged'
+ variant of the load/store instructions. This ensures that user-space
+ really did have access to the supplied memory. When addr_limit is
+ set to kernel memory the UAO bit will be set, allowing privileged
+ access to kernel memory.
+
+ Choosing this option will cause copy_to_user() et al to use user-space
+ memory permissions.
+
+ The feature is detected at runtime, the kernel will use the
+ regular load/store instructions if the cpu does not implement the
+ feature.
+
endmenu
menu "Boot options"