linux-kernel - Re: [PATCH v3] kexec: Support purgatories with .text.hot sections

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Message-ID: <CANiDSCvTMmqGxQSYcs+p7v6y-aoE0HSZLuKkHWQA1O-dpkKxqQ@mail.gmail.com>
Date:   Wed, 22 Mar 2023 21:57:28 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Ross Zwisler <zwisler@...gle.com>
Cc:     Eric Biederman <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org, Philipp Rudo <prudo@...hat.com>,
        kexec@...ts.infradead.org, Baoquan He <bhe@...hat.com>
Subject: Re: [PATCH v3] kexec: Support purgatories with .text.hot sections

HI Ross

Thanks for your review.

I think we should backport this one, in case people use old kernels
with new compilers.
If there is a v4 i will resend it with your tag and the stable tag.

Thanks!

On Wed, 22 Mar 2023 at 21:42, Ross Zwisler <zwisler@...gle.com> wrote:
>
> On Wed, Mar 22, 2023 at 08:09:21PM +0100, Ricardo Ribalda wrote:
> > Clang16 links the purgatory text in two sections:
> >
> >   [ 1] .text             PROGBITS         0000000000000000  00000040
> >        00000000000011a1  0000000000000000  AX       0     0     16
> >   [ 2] .rela.text        RELA             0000000000000000  00003498
> >        0000000000000648  0000000000000018   I      24     1     8
> >   ...
> >   [17] .text.hot.        PROGBITS         0000000000000000  00003220
> >        000000000000020b  0000000000000000  AX       0     0     1
> >   [18] .rela.text.hot.   RELA             0000000000000000  00004428
> >        0000000000000078  0000000000000018   I      24    17     8
> >
> > And both of them have their range [sh_addr ... sh_addr+sh_size] on the
> > area pointed by `e_entry`.
> >
> > This causes that image->start is calculated twice, once for .text and
> > another time for .text.hot. The second calculation leaves image->start
> > in a random location.
> >
> > Because of this, the system crashes inmediatly after:
> >
> > kexec_core: Starting new kernel
> >
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
>
> Reviewed-by: Ross Zwisler <zwisler@...gle.com>

Cc: stable@...r.kernel.org
>
> > ---
> > kexec: Fix kexec_file_load for llvm16
> >
> > When upreving llvm I realised that kexec stopped working on my test
> > platform. This patch fixes it.
> >
> > To: Eric Biederman <ebiederm@...ssion.com>
> > Cc: Baoquan He <bhe@...hat.com>
> > Cc: Philipp Rudo <prudo@...hat.com>
> > Cc: kexec@...ts.infradead.org
> > Cc: linux-kernel@...r.kernel.org
> > ---
> > Changes in v3:
> > - Fix initial value. Thanks Ross!
> > - Link to v2: https://lore.kernel.org/r/20230321-kexec_clang16-v2-0-d10e5d517869@chromium.org
> >
> > Changes in v2:
> > - Fix if condition. Thanks Steven!.
> > - Update Philipp email. Thanks Baoquan.
> > - Link to v1: https://lore.kernel.org/r/20230321-kexec_clang16-v1-0-a768fc2c7c4d@chromium.org
> > ---
> >  kernel/kexec_file.c | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> > index f1a0e4e3fb5c..25a37d8f113a 100644
> > --- a/kernel/kexec_file.c
> > +++ b/kernel/kexec_file.c
> > @@ -901,10 +901,21 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
> >               }
> >
> >               offset = ALIGN(offset, align);
> > +
> > +             /*
> > +              * Check if the segment contains the entry point, if so,
> > +              * calculate the value of image->start based on it.
> > +              * If the compiler has produced more than one .text sections
> > +              * (Eg: .text.hot), they are generally after the main .text
> > +              * section, and they shall not be used to calculate
> > +              * image->start. So do not re-calculate image->start if it
> > +              * is not set to the initial value.
> > +              */
> >               if (sechdrs[i].sh_flags & SHF_EXECINSTR &&
> >                   pi->ehdr->e_entry >= sechdrs[i].sh_addr &&
> >                   pi->ehdr->e_entry < (sechdrs[i].sh_addr
> > -                                      + sechdrs[i].sh_size)) {
> > +                                      + sechdrs[i].sh_size) &&
> > +                 kbuf->image->start == pi->ehdr->e_entry) {
> >                       kbuf->image->start -= sechdrs[i].sh_addr;
> >                       kbuf->image->start += kbuf->mem + offset;
> >               }
> >
> > ---
> > base-commit: 17214b70a159c6547df9ae204a6275d983146f6b
> > change-id: 20230321-kexec_clang16-4510c23d129c
> >
> > Best regards,
> > --
> > Ricardo Ribalda <ribalda@...omium.org>



-- 
Ricardo Ribalda