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.marinas@arm.com Cc: Will Deacon will.deacon@arm.com CC: Andrey Konovalov andreyknvl@google.com CC: Alexander Viro viro@zeniv.linux.org.uk Signed-off-by: Vincenzo Frascino vincenzo.frascino@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