linux-kernel - [patch V2 00/20] x86/fpu: Clean up exception fixups and error handling in sigframe related code

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Date:   Tue,  7 Sep 2021 21:56:12 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tony Luck <tony.luck@...el.com>,
        Song Liu <songliubraving@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Peter Ziljstra <peterz@...radead.org>
Subject: [patch V2 00/20] x86/fpu: Clean up exception fixups and error
 handling in sigframe related code

A recent discussion [1] about hardware poisoning unearthed some short
comings in the error handling of the sigframe related FPU code:

  - The error exit for exceptions other than #PF is obfuscated

  - The error code return values of the various functions are pointless
    because all callers just care about success or failure and the error
    codes are never propagated to user space.

  - Some of the buffer clearing happens needlessly inside of page fault
    disabled regions.

The discussion around V1 of this series which can be found here:

  https://lore.kernel.org/r/20210830154702.247681585@linutronix.de

identified a few more issues especially in the area of exception fixups:

  - The MCE aware exception fixup is inconsistent and confusing especially
    in copy_mc_64.c. It uses a fixup function which stores the trap number
    in regs->ax just to overwrite regs->ax at the callsite specific fixup.

The following series cleans this up. The resulting excecutable code is
slightly smaller with that.

It's also available in git:

    git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git x86/fpu

Changes vs. V1:

  - Deduplicate the exception table related code

  - Change the exception table store to use a fixup type identifier instead
    of a function pointer. That allows to use the same fixup function for
    different types and avoids adding new global functions and exports to
    solve the identified issues. This makes the cleanup of the odd fixup
    functions in copy_mc_64 and the fpu code simpler

  - Make copy_mc_64 and FPU code use the new fixup type mechanics

  - Remove #MC handling from the various *SAVE functions which write the
    FPU registers to the user space sigframe as these can't raise #MC
    according to Tony.

  - Address a few review comments and adjust the patches to the new
    exception table mechanism.

Thanks,

	tglx

[1] https://lore.kernel.org/r/87r1edgs2w.ffs@tglx

---
 arch/x86/ia32/ia32_signal.c                |   14 +-
 arch/x86/include/asm/asm.h                 |   49 ++++-----
 arch/x86/include/asm/extable.h             |   44 +++++---
 arch/x86/include/asm/extable_fixup_types.h |   22 ++++
 arch/x86/include/asm/fpu/internal.h        |   84 ++++++++++------
 arch/x86/include/asm/msr.h                 |    4 
 arch/x86/include/asm/segment.h             |    2 
 arch/x86/kernel/cpu/mce/core.c             |   40 ++------
 arch/x86/kernel/cpu/mce/internal.h         |   14 --
 arch/x86/kernel/cpu/mce/severity.c         |   22 ++--
 arch/x86/kernel/fpu/signal.c               |  145 +++++++++++++++--------------
 arch/x86/kernel/signal.c                   |   18 +--
 arch/x86/lib/copy_mc_64.S                  |    8 -
 arch/x86/mm/extable.c                      |  131 ++++++++++----------------
 arch/x86/net/bpf_jit_comp.c                |   11 --
 scripts/sorttable.c                        |    4 
 16 files changed, 302 insertions(+), 310 deletions(-)