Document the changes in Documentation/arm64/tagged-pointers.txt.
Signed-off-by: Andrey Konovalov firstname.lastname@example.org --- Documentation/arm64/tagged-pointers.txt | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-)
diff --git a/Documentation/arm64/tagged-pointers.txt b/Documentation/arm64/tagged-pointers.txt index a25a99e82bb1..f4cf1f5cf362 100644 --- a/Documentation/arm64/tagged-pointers.txt +++ b/Documentation/arm64/tagged-pointers.txt @@ -17,13 +17,22 @@ this byte for application use. Passing tagged addresses to the kernel --------------------------------------
-All interpretation of userspace memory addresses by the kernel assumes -an address tag of 0x00. +The kernel supports tags in pointer arguments (including pointers in +structures) for a limited set of syscalls, the exceptions are:
-This includes, but is not limited to, addresses found in: + - memory syscalls: brk, madvise, mbind, mincore, mlock, mlock2, move_pages, + mprotect, mremap, msync, munlock, munmap, pkey_mprotect, process_vm_readv, + process_vm_writev, remap_file_pages;
- - pointer arguments to system calls, including pointers in structures - passed to system calls, + - ioctls that accept user pointers that describe virtual memory ranges; + + - TCP_ZEROCOPY_RECEIVE setsockopt. + +The kernel supports tags in user fault addresses. However the fault_address +field in the sigcontext struct will contain an untagged address. + +All other interpretations of userspace memory addresses by the kernel +assume an address tag of 0x00, in particular:
- the stack pointer (sp), e.g. when interpreting it to deliver a signal, @@ -33,11 +42,7 @@ This includes, but is not limited to, addresses found in:
Using non-zero address tags in any of these locations may result in an error code being returned, a (fatal) signal being raised, or other modes -of failure. - -For these reasons, passing non-zero address tags to the kernel via -system calls is forbidden, and using a non-zero address tag for sp is -strongly discouraged. +of failure. Using a non-zero address tag for sp is strongly discouraged.
Programs maintaining a frame pointer and frame records that use non-zero address tags may suffer impaired or inaccurate debug and profiling