On Tue, Jun 09, 2020 at 01:04:25PM +0200, Michael Kerrisk (man-pages) wrote: > Do we have any review comments for this (extensive!) patch from Dave? (Adding Andrey, since he was involved with this ABI) Regardless, it would be good to have Catalin's ack and I think he was planning to take a look at this. Will > On 5/27/20 11:17 PM, Dave Martin wrote: > > ** This patch is a draft for review and should not be applied before it > > has been discussed. ** > > > > Add documentation for the the PR_SET_TAGGED_ADDR_CTRL and > > PR_GET_TAGGED_ADDR_CTRL prctls added in Linux 5.4 for arm64. > > > > Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx> > > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > > Cc: Will Deacon <will@xxxxxxxxxx> > > Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> > > --- > > > > man2/prctl.2 | 156 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 156 insertions(+) > > > > diff --git a/man2/prctl.2 b/man2/prctl.2 > > index 3ee2702..062fd51 100644 > > --- a/man2/prctl.2 > > +++ b/man2/prctl.2 > > @@ -1504,6 +1504,143 @@ For more information, see the kernel source file > > (or > > .I Documentation/arm64/sve.txt > > before Linux 5.3). > > +.\" prctl PR_SET_TAGGED_ADDR_CTRL > > +.\" commit 63f0c60379650d82250f22e4cf4137ef3dc4f43d > > +.TP > > +.BR PR_SET_TAGGED_ADDR_CTRL " (since Linux 5.4, only on arm64)" > > +Controls support for passing tagged userspace addresses to the kernel > > +(i.e., addresses where bits 56\(em63 are not all zero). > > +.IP > > +The level of support is selected by > > +.IR "(unsigned int) arg2" , > > +which can be one of the following: > > +.RS > > +.TP > > +.B 0 > > +Addresses that are passed > > +for the purpose of being dereferenced by the kernel > > +must be untagged. > > +.TP > > +.B PR_TAGGED_ADDR_ENABLE > > +Addresses that are passed > > +for the purpose of being dereferenced by the kernel > > +may be tagged, with the exceptions summarized below. > > +.RE > > +.IP > > +The remaining arguments > > +.IR arg3 ", " arg4 " and " arg5 > > +must all be zero. > > +.IP > > +On success, the mode specified in > > +.I arg2 > > +is set for the calling thread and the the return value is 0. > > +If the arguments are invalid, > > +the mode specified in > > +.I arg2 > > +is unrecognized, > > +or if this feature is disabled or unsupported by the kernel, > > +the call fails with > > +.BR EINVAL . > > +.IP > > +In particular, if > > +.BR prctl ( PR_SET_TAGGED_ADDR_CTRL , > > +0, 0, 0, 0) > > +fails with > > +.B EINVAL > > +then all addresses passed to the kernel must be untagged. > > +.IP > > +Irrespective of which mode is set, > > +addresses passed to certain interfaces > > +must always be untagged: > > +.RS > > +.IP \(em > > +.BR brk (2), > > +.BR mmap (2), > > +.BR shmat (2), > > +and the > > +.I new_address > > +argument of > > +.BR mremap (2). > > +.IP > > +(Prior to Linux 5.6 these accepted tagged addresses, > > +but the behaviour may not be what you expect. > > +Don't rely on it.) > > +.IP \(em > > +\(oqpolymorphic\(cq interfaces > > +that accept pointers to arbitrary types cast to a > > +.I void * > > +or other generic type, specifically > > +.BR prctl (2), > > +.BR ioctl (2), > > +and in general > > +.BR setsockopt (2) > > +(only certain specific > > +.BR setsockopt (2) > > +options allow tagged addresses). > > +.IP \(em > > +.BR shmdt (2). > > +.RE > > +.IP > > +This list of exclusions may shrink > > +when moving from one kernel version to a later kernel version. > > +While the kernel may make some guarantees > > +for backwards compatibility reasons, > > +for the purposes of new software > > +the effect of passing tagged addresses to these interfaces > > +is unspecified. > > +.IP > > +The mode set by this call is inherited across > > +.BR fork (2) > > +and > > +.BR clone (2). > > +The mode is reset by > > +.BR execve (2) > > +to 0 > > +(i.e., tagged addresses not permitted in the user/kernel ABI). > > +.IP > > +.B Warning: > > +Because the compiler or run-time environment > > +may make use of address tagging, > > +a successful > > +.B PR_SET_TAGGED_ADDR_CTRL > > +may crash the calling process. > > +The conditions for using it safely are complex and system-dependent. > > +Don't use it unless you know what you are doing. > > +.IP > > +For more information, see the kernel source file > > +.IR Documentation/arm64/tagged\-address\-abi.rst . > > +.\" prctl PR_GET_TAGGED_ADDR_CTRL > > +.\" commit 63f0c60379650d82250f22e4cf4137ef3dc4f43d > > +.TP > > +.BR PR_GET_TAGGED_ADDR_CTRL " (since Linux 5.4, only on arm64)" > > +Returns the current tagged address mode > > +for the calling thread. > > +.IP > > +Arguments > > +.IR arg2 ", " arg3 ", " arg4 " and " arg5 > > +must all be zero. > > +.IP > > +If the arguments are invalid > > +or this feature is disabled or unsupported by the kernel, > > +the call fails with > > +.BR EINVAL . > > +In particular, if > > +.BR prctl ( PR_GET_TAGGED_ADDR_CTRL , > > +0, 0, 0, 0) > > +fails with > > +.BR EINVAL , > > +then this feature is definitely unsupported or disabled, > > +and all addresses passed to the kernel must be untagged. > > +.IP > > +Otherwise, the call returns a nonnegative value > > +describing the current tagged address mode, > > +encoded in the same way as the > > +.I arg2 > > +argument of > > +.BR PR_SET_TAGGED_ADDR_CTRL . > > +.IP > > +For more information, see the kernel source file > > +.IR Documentation/arm64/tagged\-address\-abi.rst . > > .\" > > .\" prctl PR_TASK_PERF_EVENTS_DISABLE > > .TP > > @@ -1749,6 +1886,7 @@ On success, > > .BR PR_GET_SPECULATION_CTRL , > > .BR PR_SVE_GET_VL , > > .BR PR_SVE_SET_VL , > > +.BR PR_GET_TAGGED_ADDR_CTRL , > > .BR PR_GET_THP_DISABLE , > > .BR PR_GET_TIMING , > > .BR PR_GET_TIMERSLACK , > > @@ -2057,6 +2195,24 @@ is > > .B PR_SVE_GET_VL > > and SVE is not available on this platform. > > .TP > > +.B EINVAL > > +.I option > > +is > > +.BR PR_SET_TAGGED_ADDR_CTRL > > +and the arguments are invalid or unsupported. > > +See the description of > > +.B PR_SET_TAGGED_ADDR_CTRL > > +above for details. > > +.TP > > +.B EINVAL > > +.I option > > +is > > +.BR PR_GET_TAGGED_ADDR_CTRL > > +and the arguments are invalid or unsupported. > > +See the description of > > +.B PR_GET_TAGGED_ADDR_CTRL > > +above for details. > > +.TP > > .B ENODEV > > .I option > > was > > > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/
