Document the changes in Documentation/arm64/tagged-pointers.txt.
Signed-off-by: Andrey Konovalov andreyknvl@google.com --- Documentation/arm64/tagged-pointers.txt | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/Documentation/arm64/tagged-pointers.txt b/Documentation/arm64/tagged-pointers.txt index a25a99e82bb1..ae877d185fdb 100644 --- a/Documentation/arm64/tagged-pointers.txt +++ b/Documentation/arm64/tagged-pointers.txt @@ -17,13 +17,21 @@ 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. +Some initial work for supporting non-zero address tags passed to the +kernel has been done. As of now, the kernel supports tags in:
-This includes, but is not limited to, addresses found in: + - user fault addresses
- - pointer arguments to system calls, including pointers in structures - passed to system calls, + - pointer arguments (including pointers in structures), which don't + describe virtual memory ranges, passed to system calls + +All other interpretations of userspace memory addresses by the kernel +assume an address tag of 0x00. This includes, but is not limited to, +addresses found in: + + - pointer arguments (including pointers in structures), which describe + virtual memory ranges, passed to memory system calls (mmap, mprotect, + etc.)
- the stack pointer (sp), e.g. when interpreting it to deliver a signal, @@ -33,11 +41,7 @@ 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