[Bug runtime/30456] New: Kernel 5.18+ retired set_fs() and replaced it with the user_access_begin/end() pair for userland memory accesses

[Bug runtime/30456] New: Kernel 5.18+ retired set_fs() and replaced it with the user_access_begin/end() pair for userland memory accesses

[agentzh at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30456

            Bug ID: 30456
           Summary: Kernel 5.18+ retired set_fs() and replaced it with the
                    user_access_begin/end() pair for userland memory
                    accesses
           Product: systemtap
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: agentzh at gmail dot com
  Target Milestone: ---

Currently, the stap runtime does nothing for kernel 5.18+ without set_fs(),
which is wrong at least on x86 for userland accesses.

I'm preparing a fix by switching to the new replacement API,
user_access_begin() and user_access_end().

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[Bug runtime/30456] Kernel 5.18+ retired set_fs() and replaced it with the user_access_begin/end() pair for userland memory accesses

[agentzh at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30456

--- Comment #1 from agentzh <agentzh at gmail dot com> ---
I'd propose this patch to address this issue:
https://gist.github.com/agentzh/0628614ac04f773c6662d225100924be

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[Bug runtime/30456] Kernel 5.18+ retired set_fs() and replaced it with the user_access_begin/end() pair for userland memory accesses

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30456

Frank Ch. Eigler <fche at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fche at redhat dot com

--- Comment #2 from Frank Ch. Eigler <fche at redhat dot com> ---
unfortunately, this triggers bug #30716

It appears that if we're going to use the stac/clac wrappers around calls to
user-space access functions at all, those functions must be chosen from a
whitelist.

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[Bug runtime/30456] Kernel 5.18+ retired set_fs() and replaced it with the user_access_begin/end() pair for userland memory accesses

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30456

Frank Ch. Eigler <fche at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #3 from Frank Ch. Eigler <fche at redhat dot com> ---
commit a9337abbb213e82e919e67150b31399cc49c469f
Author: Yichun Zhang (agentzh) <yichun@openresty.com>
Date:   Tue May 16 17:17:07 2023 -0700

    PR30456: kernel 5.18+ removed set_fs() and we should use the new
replacement, user_access_begin()/user_access_end() for userland memory
accesses.

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