linux-kernel - Re: [PATCH] x86/cmdline: Disable jump tables for cmdline.c

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Date:   Mon, 21 Dec 2020 13:40:44 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/cmdline: Disable jump tables for cmdline.c

On Mon, Dec 21, 2020 at 1:23 PM Arvind Sankar <nivedita@...m.mit.edu> wrote:
>
> On Mon, Dec 21, 2020 at 11:14:39AM -0800, Nick Desaulniers wrote:
> > On Wed, Sep 2, 2020 at 7:31 PM Arvind Sankar <nivedita@...m.mit.edu> wrote:
> > >
> > > When CONFIG_RETPOLINE is disabled, Clang uses a jump table for the
> > > switch statement in cmdline_find_option (jump tables are disabled when
> > > CONFIG_RETPOLINE is enabled). This function is called very early in boot
> > > from sme_enable() if CONFIG_AMD_MEM_ENCRYPT is enabled. At this time,
> >
> > Hi Arvind, sorry I missed this when you first sent it.  I'm going
> > through and mass deleting my inbox (email bankruptcy) but noticed
> > this.  I couldn't reproduce jump tables in cmdline_find_option with
> > CONFIG_RETPOLINE disabled but CONFIG_AMD_MEM_ENCRYPT on today's
> > linux-next. Can you please confirm that this is still an issue? I will
> > reread the disassembly, but it looks like a bunch of cmp/test+jumps.
> >
>
> The patch got merged and is in v5.10 -- are you testing with it reverted
> or just plain linux-next?

Oh, sorry, I missed any email that it was merged (and didn't look in
git log).  Just linux-next, so no wonder I didn't see any jump tables.
:^P

-- 
Thanks,
~Nick Desaulniers