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x86/kexec: Fix location of relocate_kernel with -ffunction-sections

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After commit

  cb33ff9e06 ("x86/kexec: Move relocate_kernel to kernel .data section"),

kernels configured with an option that uses -ffunction-sections, such as
CONFIG_LTO_CLANG, crash when kexecing because the value of relocate_kernel
does not match the value of __relocate_kernel_start so incorrect code gets
copied via machine_kexec_prepare().

  $ llvm-nm good-vmlinux &| rg relocate_kernel
  ffffffff83280d41 T __relocate_kernel_end
  ffffffff83280b00 T __relocate_kernel_start
  ffffffff83280b00 T relocate_kernel

  $ llvm-nm bad-vmlinux &| rg relocate_kernel
  ffffffff83266100 D __relocate_kernel_end
  ffffffff83266100 D __relocate_kernel_start
  ffffffff8120b0d8 T relocate_kernel

When -ffunction-sections is enabled, TEXT_MAIN matches on
'.text.[0-9a-zA-Z_]*' to coalesce the function specific functions back
into .text during link time after they have been optimized. Due to the
placement of TEXT_TEXT before KEXEC_RELOCATE_KERNEL in the x86 linker
script, the .text.relocate_kernel section ends up in .text instead of
.data.

Use a second dot in the relocate_kernel section name to avoid matching
on TEXT_MAIN, which matches a similar situation that happened in
commit

  79cd2a1122 ("x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG"),

which allows kexec to function properly.

While .data.relocate_kernel still ends up in the .data section via
DATA_MAIN -> DATA_DATA, ensure it is located with the
.text.relocate_kernel section as intended by performing the same
transformation.

Fixes: cb33ff9e06 ("x86/kexec: Move relocate_kernel to kernel .data section")
Fixes: 8dbec5c77b ("x86/kexec: Add data section to relocate_kernel")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250109140757.2841269-6-dwmw2@infradead.org
This commit is contained in:
Nathan Chancellor
2025-01-09 14:04:17 +00:00
committed by Borislav Petkov (AMD)
parent 2cacf7f23a
commit eeed915041
2 changed files with 5 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
arch/x86/kernel/relocate_kernel_64.S
View File

@@ -23,11 +23,11 @@
#define PAGE_ATTR (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY)
/*
* The .text.relocate_kernel and .data.relocate_kernel sections are copied
* The .text..relocate_kernel and .data..relocate_kernel sections are copied
* into the control page, and the remainder of the page is used as the stack.
*/
.section .data.relocate_kernel,"a";
.section .data..relocate_kernel,"a";
/* Minimal CPU state */
SYM_DATA_LOCAL(saved_rsp, .quad 0)
SYM_DATA_LOCAL(saved_cr0, .quad 0)
@@ -39,7 +39,7 @@ SYM_DATA(kexec_pa_table_page, .quad 0)
SYM_DATA(kexec_pa_swap_page, .quad 0)
SYM_DATA_LOCAL(pa_backup_pages_map, .quad 0)
.section .text.relocate_kernel,"ax";
.section .text..relocate_kernel,"ax";
.code64
SYM_CODE_START_NOALIGN(relocate_kernel)
UNWIND_HINT_END_OF_STACK

4
arch/x86/kernel/vmlinux.lds.S
View File

@@ -100,8 +100,8 @@ const_pcpu_hot = pcpu_hot;
#define KEXEC_RELOCATE_KERNEL \
. = ALIGN(0x100); \
__relocate_kernel_start = .; \
*(.text.relocate_kernel); \
*(.data.relocate_kernel); \
*(.text..relocate_kernel); \
*(.data..relocate_kernel); \
__relocate_kernel_end = .;
ASSERT(__relocate_kernel_end - __relocate_kernel_start <= KEXEC_CONTROL_CODE_MAX_SIZE,