Hi Ricardo,
On Thu, 30 Mar 2023 11:44:47 +0200 Ricardo Ribalda ribalda@chromium.org 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@vger.kernel.org Fixes: 930457057abe ("kernel/kexec_file.c: split up __kexec_load_puragory") Reviewed-by: Ross Zwisler zwisler@google.com Signed-off-by: Ricardo Ribalda ribalda@chromium.org
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.*/
+ 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@redhat.com
kbuf->image->start -= sechdrs[i].sh_addr; kbuf->image->start += kbuf->mem + offset; }