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Message-ID: <CANiDSCsbmmkfRGC-GvhX-RSZGU0CT7ZqLo6Z=RmccoM7zbPcsA@mail.gmail.com>
Date: Thu, 30 Mar 2023 11:47:14 +0200
From: Ricardo Ribalda <ribalda@...omium.org>
To: Simon Horman <horms@...nel.org>
Cc: Eric Biederman <ebiederm@...ssion.com>,
linux-kernel@...r.kernel.org, Baoquan He <bhe@...hat.com>,
stable@...r.kernel.org, Ross Zwisler <zwisler@...gle.com>,
Philipp Rudo <prudo@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>, kexec@...ts.infradead.org
Subject: Re: [PATCH v4 1/2] kexec: Support purgatories with .text.hot sections
Hi Simon
Thanks for your review!
On Thu, 30 Mar 2023 at 09:49, Simon Horman <horms@...nel.org> wrote:
>
> On Mon, Mar 27, 2023 at 05:06:53PM +0200, 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:
>
> s/inmediatly/immediately/
>
> >
> > kexec_core: Starting new kernel
> >
> > Cc: stable@...r.kernel.org
>
> Maybe a fixes tag is warranted here.
>
> > Reviewed-by: Ross Zwisler <zwisler@...gle.com>
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.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
>
> nit: s/sections/section/
>
> > + * (Eg: .text.hot), they are generally after the main .text
>
> If this is the general case, then are there cases where this doesn't hold?
When looking at this issue, I have only seen .text.hot after .text.
But I cannot warantee that future versions of llvm or gcc decide to
swap the order.
I am going to add a WARN whenever there are two overlapping .text
sections so the user has the chance to update their linker script.
>
> > + * 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;
> > }
> >
> > --
> > 2.40.0.348.gf938b09366-goog-b4-0.11.0-dev-696ae
> >
> > _______________________________________________
> > kexec mailing list
> > kexec@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
> >
--
Ricardo Ribalda
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