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

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Message-Id: <20230321-kexec_clang16-v1-0-a768fc2c7c4d@chromium.org>
Date:   Tue, 21 Mar 2023 12:49:08 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Eric Biederman <ebiederm@...ssion.com>
Cc:     Philipp Rudo <prudo@...ux.vnet.ibm.com>,
        Ricardo Ribalda <ribalda@...omium.org>,
        linux-kernel@...r.kernel.org, kexec@...ts.infradead.org
Subject: [PATCH] kexec: Support purgatories with .text.hot sections

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>
---
kexec: Support purgatories with .text.hot sections

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

To: Eric Biederman <ebiederm@...ssion.com>
Cc: Philipp Rudo <prudo@...ux.vnet.ibm.com>
Cc: kexec@...ts.infradead.org
Cc: linux-kernel@...r.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) {
 			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>