On exception entry, the kernel explicitly resets the PSTATE.TCO (tag
check override) so that any kernel memory accesses will be checked (the
bit is restored on exception return). This has the side-effect that the
uaccess routines will not honour the PSTATE.TCO that may have been set
by the user prior to a syscall.
There is no issue in practice since PSTATE.TCO is expected to be used
only for brief periods in specific routines (e.g. garbage collection).
To control the tag checking mode of the uaccess routines, the user will
have to invoke a corresponding prctl() call.
Document the kernel behaviour w.r.t. PSTATE.TCO accordingly.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Fixes: df9d7a22dd ("arm64: mte: Add Memory Tagging Extension documentation")
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Szabolcs Nagy <szabolcs.nagy@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
We offer both PTRACE_PEEKMTETAGS and PTRACE_POKEMTETAGS requests via
ptrace().
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Memory Tagging Extension (part of the ARMv8.5 Extensions) provides
a mechanism to detect the sources of memory related errors which
may be vulnerable to exploitation, including bounds violations,
use-after-free, use-after-return, use-out-of-scope and use before
initialization errors.
Add Memory Tagging Extension documentation for the arm64 linux
kernel support.
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Co-developed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc: Will Deacon <will@kernel.org>
Peter Collingbourne