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authorVincenzo Frascino <vincenzo.frascino@arm.com>2019-04-15 12:49:37 +0300
committerWill Deacon <will.deacon@arm.com>2019-04-23 20:01:58 +0300
commitaf1b3cf2c2a3f42bbb680812ff1bbd715ac8af69 (patch)
tree67550d4018c6cc1e368214556d744317da53e689 /arch/arm64/Kconfig
parent1255a7341bee6cd96df056ed0c13e44b59023687 (diff)
downloadlinux-af1b3cf2c2a3f42bbb680812ff1bbd715ac8af69.tar.xz
arm64: compat: Add KUSER_HELPERS config option
When kuser helpers are enabled the kernel maps the relative code at a fixed address (0xffff0000). Making configurable the option to disable them means that the kernel can remove this mapping and any access to this memory area results in a sigfault. Add a KUSER_HELPERS config option that can be used to disable the mapping when it is turned off. This option can be turned off if and only if the applications are designed specifically for the platform and they do not make use of the kuser helpers code. Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> [will: Use IS_ENABLED() instead of #ifdef] Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/Kconfig')
-rw-r--r--arch/arm64/Kconfig28
1 files changed, 28 insertions, 0 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index c383625ec02c..0861a6f5ee4a 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1498,6 +1498,34 @@ config COMPAT
If you want to execute 32-bit userspace applications, say Y.
+config KUSER_HELPERS
+ bool "Enable kuser helpers page for 32 bit applications."
+ depends on COMPAT
+ default y
+ help
+ Warning: disabling this option may break 32-bit user programs.
+
+ Provide kuser helpers to compat tasks. The kernel provides
+ helper code to userspace in read only form at a fixed location
+ to allow userspace to be independent of the CPU type fitted to
+ the system. This permits binaries to be run on ARMv4 through
+ to ARMv8 without modification.
+
+ See Documentation/arm/kernel_user_helpers.txt for details.
+
+ However, the fixed address nature of these helpers can be used
+ by ROP (return orientated programming) authors when creating
+ exploits.
+
+ If all of the binaries and libraries which run on your platform
+ are built specifically for your platform, and make no use of
+ these helpers, then you can turn this option off to hinder
+ such exploits. However, in that case, if a binary or library
+ relying on those helpers is run, it will not function correctly.
+
+ Say N here only if you are absolutely certain that you do not
+ need these helpers; otherwise, the safe option is to say Y.
+
config SYSVIPC_COMPAT
def_bool y
depends on COMPAT && SYSVIPC