Re: [PATCH] kexec: Support purgatories with .text.hot sections

From: Ricardo Ribalda <ribalda@chromium.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Eric Biederman <ebiederm@xmission.com>,
	Philipp Rudo <prudo@linux.vnet.ibm.com>,
	 linux-kernel@vger.kernel.org, kexec@lists.infradead.org
Subject: Re: [PATCH] kexec: Support purgatories with .text.hot sections
Date: Wed, 22 Mar 2023 15:42:14 +0100	[thread overview]
Message-ID: <CANiDSCt_wvaHBq-Yss0QaKTtefBhWwtahFO8_jw6CPSvBwbbMg@mail.gmail.com> (raw)
In-Reply-To: <ZBsSBr87al9ccG96@home.goodmis.org>

Hi Steven

On Wed, 22 Mar 2023 at 15:34, Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Tue, Mar 21, 2023 at 12:49:08PM +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@chromium.org>
> > To: Eric Biederman <ebiederm@xmission.com>
> > Cc: Philipp Rudo <prudo@linux.vnet.ibm.com>
> > Cc: kexec@lists.infradead.org
> > Cc: linux-kernel@vger.kernel.org
> > ---
> >  kernel/kexec_file.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> > index f1a0e4e3fb5c..b1a25d97d5e2 100644
> > --- a/kernel/kexec_file.c
> > +++ b/kernel/kexec_file.c
> > @@ -904,7 +904,8 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
> >               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_shnum) {
>
> Shouldn't this be: kbuf->image->start == pi->ehdr->e_shnum) {

You are absolutely right, I screwed up when I ported the code from my
test tree to the tree that I use for upstreaming.
Instead of removing all the printks I wrote code.

:S

Will resend the patch

>
> ?
>
> As you want to only do this update when it's not equal to the initial value.
> If this did work, then you may want to make sure that was the initial value.
>
> Also, please add a comment about why you are doing this check.
>
> Thanks!
>
> -- Steve
>
> >                       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@chromium.org>

-- 
Ricardo Ribalda

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