A couple of minor nits below.
On Wed, Jun 12, 2019 at 03:21:11PM +0100, Vincenzo Frascino wrote:
--- a/Documentation/arm64/tagged-pointers.txt +++ b/Documentation/arm64/tagged-pointers.txt @@ -18,7 +18,8 @@ Passing tagged addresses to the kernel
All interpretation of userspace memory addresses by the kernel assumes -an address tag of 0x00. +an address tag of 0x00, unless the userspace opts-in the ARM64 Tagged +Address ABI via the PR_SET_TAGGED_ADDR_CTRL prctl(). This includes, but is not limited to, addresses found in: @@ -31,18 +32,23 @@ This includes, but is not limited to, addresses found in:
- the frame pointer (x29) and frame records, e.g. when interpreting them to generate a backtrace or call graph.
-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. +Using non-zero address tags in any of these locations when the +userspace application did not opt-in to the ARM64 Tagged Address ABI,
Nitpick: drop the comma after "ABI," since a predicate follows.
+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. +For these reasons, when the userspace application did not opt-in, 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. Programs maintaining a frame pointer and frame records that use non-zero address tags may suffer impaired or inaccurate debug and profiling visibility. +A definition of the meaning of ARM64 Tagged Address ABI and of the +guarantees that the ABI provides when the userspace opts-in via prctl() +can be found in: Documentation/arm64/tagged-address-abi.txt.
Preserving tags
@@ -57,6 +63,9 @@ be preserved. The architecture prevents the use of a tagged PC, so the upper byte will be set to a sign-extension of bit 55 on exception return. +This behaviours are preserved even when the the userspace opts-in the ARM64
"These" ... "opts in to"
+Tagged Address ABI via the PR_SET_TAGGED_ADDR_CTRL prctl().
Other considerations
-- 2.21.0