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
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