On arm64 the TCR_EL1.TBI0 bit has been always enabled on the arm64 kernel, hence the userspace (EL0) is allowed to set a non-zero value in the top byte but the resulting pointers are not allowed at the user-kernel syscall ABI boundary.
This patchset proposes a relaxation of the ABI with which it is possible to pass tagged tagged pointers to the syscalls, when these pointers are in memory ranges obtained as described in tagged-address-abi.txt contained in this patch series. Since it is not desirable to relax the ABI to allow tagged user addresses into the kernel indiscriminately, this patchset documents a new sysctl interface (/proc/sys/abi/tagged_addr) that is used to prevent the applications from enabling the relaxed ABI and a new prctl() interface that can be used to enable or disable the relaxed ABI. This patchset should be merged together with [1]. [1] https://patchwork.kernel.org/cover/10674351/ Cc: Catalin Marinas <catalin.mari...@arm.com> Cc: Will Deacon <will.dea...@arm.com> CC: Andrey Konovalov <andreyk...@google.com> CC: Alexander Viro <v...@zeniv.linux.org.uk> Signed-off-by: Vincenzo Frascino <vincenzo.frasc...@arm.com> Vincenzo Frascino (2): arm64: Define Documentation/arm64/tagged-address-abi.txt arm64: Relax Documentation/arm64/tagged-pointers.txt Documentation/arm64/tagged-address-abi.txt | 111 +++++++++++++++++++++ Documentation/arm64/tagged-pointers.txt | 23 +++-- 2 files changed, 127 insertions(+), 7 deletions(-) create mode 100644 Documentation/arm64/tagged-address-abi.txt -- 2.21.0
