Hi Ricardo,
On Thu, 30 Mar 2023 11:44:47 +0200
Ricardo Ribalda <ribalda@xxxxxxxxxxxx> 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 immediately after:
>
> kexec_core: Starting new kernel
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 930457057abe ("kernel/kexec_file.c: split up __kexec_load_puragory")
> Reviewed-by: Ross Zwisler <zwisler@xxxxxxxxxx>
> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> ---
> kernel/kexec_file.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index f1a0e4e3fb5c..c7a0e51a6d87 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -901,10 +901,22 @@ 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 section
> + * (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, and warn the user so they
> + * have a chance to fix their purgatory's linker script.
> + */
> 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) &&
> + !WARN_ON(kbuf->image->start != pi->ehdr->e_entry)) {
Looks good to me. I'm not sure if it is better to use WARN_ON_ONCE to
avoid spamming the log when there are more than two .text sections or
when you reload the kernel. But that's only a rare corner case. So no
strong opinion from my side. Either way
Reviewed-by: Philipp Rudo <prudo@xxxxxxxxxx>
> kbuf->image->start -= sechdrs[i].sh_addr;
> kbuf->image->start += kbuf->mem + offset;
> }
>
