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vmlinux.lds.h: Handle decrypted data section with !SMP

PATCH Applied Nathan Chancellor 3 participants 3 messages May 6, 2021 – Jun 4, 2021 Generic include/asm header files

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Nathan Chancellor

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PATCH 1/1 vmlinux.lds.h: Handle decrypted data section with !SMP

With x86_64_defconfig and the following configs, there is an orphan section warning:

CONFIG_SMP=n
CONFIG_AMD_MEM_ENCRYPT=y
CONFIG_HYPERVISOR_GUEST=y
CONFIG_KVM=y
CONFIG_PARAVIRT=y

ld: warning: orphan section .data..decrypted' from arch/x86/kernel/cpu/vmware.o' being placed in section `.data..decrypted'
ld: warning: orphan section .data..decrypted' from arch/x86/kernel/kvm.o' being placed in section `.data..decrypted'

These sections are created with DEFINE_PER_CPU_DECRYPTED, which ultimately turns into __PCPU_ATTRS, which in turn has a section attribute with a value of PER_CPU_BASE_SECTION + the section name. When CONFIG_SMP is not set, the base section is .data and that is not currently handled in any linker script.

Add .data..decrypted to PERCPU_DECRYPTED_SECTION, which is included in PERCPU_INPUT -> PERCPU_SECTION, which is include in the x86 linker script when either CONFIG_X86_64 or CONFIG_SMP is unset, taking care of the warning.

Fixes ac26963a1175 ("percpu: Introduce DEFINE_PER_CPU_DECRYPTED")
Link https://github.com/ClangBuiltLinux/linux/issues/1360
Reported-by kernel test robot <[email protected]>
Signed-off-by Nathan Chancellor <[email protected]>

---

I took the simple fix route with this patch since I highly doubt someone is actually running a CONFIG_AMD_MEM_ENCRYPT=y + CONFIG_SMP=n kernel. If this section should actually be in .data, I can respin.

 include/asm-generic/vmlinux.lds.h | 1 +
 1 file changed, 1 insertion(+)
include/asm-generic/vmlinux.lds.h +1 -0
index 40a9c101565e..17325416e2de 100644
@@ -960,6 +960,7 @@
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 #define PERCPU_DECRYPTED_SECTION					\
 	. = ALIGN(PAGE_SIZE);						\
+	*(.data..decrypted)						\
 	*(.data..percpu..decrypted)					\
 	. = ALIGN(PAGE_SIZE);
 #else

base-commit: 8404c9fbc84b741f66cff7d4934a25dd2c344452

Signature · 1 line
2.31.1.442.g7e39198978
Reviewed-by Tested-by on v1 1/1
#1 lore raw
Quoted 24 lines · Nathan Chancellor

With x86_64_defconfig and the following configs, there is an orphan section warning:

CONFIG_SMP=n
CONFIG_AMD_MEM_ENCRYPT=y
CONFIG_HYPERVISOR_GUEST=y
CONFIG_KVM=y
CONFIG_PARAVIRT=y

ld: warning: orphan section .data..decrypted' from arch/x86/kernel/cpu/vmware.o' being placed in section `.data..decrypted'
ld: warning: orphan section .data..decrypted' from arch/x86/kernel/kvm.o' being placed in section `.data..decrypted'

These sections are created with DEFINE_PER_CPU_DECRYPTED, which ultimately turns into __PCPU_ATTRS, which in turn has a section attribute with a value of PER_CPU_BASE_SECTION + the section name. When CONFIG_SMP is not set, the base section is .data and that is not currently handled in any linker script.

Add .data..decrypted to PERCPU_DECRYPTED_SECTION, which is included in PERCPU_INPUT -> PERCPU_SECTION, which is include in the x86 linker script when either CONFIG_X86_64 or CONFIG_SMP is unset, taking care of the warning.

Quoted 4 lines
Fixes ac26963a1175 ("percpu: Introduce DEFINE_PER_CPU_DECRYPTED")
Link https://github.com/ClangBuiltLinux/linux/issues/1360
Reported-by kernel test robot <[email protected]>
Signed-off-by Nathan Chancellor <[email protected]>

Thanks for the patch; LGTM.

Reviewed-by Nick Desaulniers <[email protected]>
Tested-by Nick Desaulniers <[email protected]> # build
Quoted 26 lines

---

I took the simple fix route with this patch since I highly doubt someone is actually running a CONFIG_AMD_MEM_ENCRYPT=y + CONFIG_SMP=n kernel. If this section should actually be in .data, I can respin.

 include/asm-generic/vmlinux.lds.h | 1 +
 1 file changed, 1 insertion(+)
include/asm-generic/vmlinux.lds.h +1 -0
index 40a9c101565e..17325416e2de 100644
@@ -960,6 +960,7 @@
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 #define PERCPU_DECRYPTED_SECTION                                       \
        . = ALIGN(PAGE_SIZE);                                           \
+       *(.data..decrypted)                                             \
        *(.data..percpu..decrypted)                                     \
        . = ALIGN(PAGE_SIZE);
 #else

base-commit: 8404c9fbc84b741f66cff7d4934a25dd2c344452 --
2.31.1.442.g7e39198978

Signature · 2 lines
Thanks,
~Nick Desaulniers
Applied
#2 lore raw
In reply to Nathan Chancellor
Quoted 10 lines · Nathan Chancellor

With x86_64_defconfig and the following configs, there is an orphan section warning:

CONFIG_SMP=n
CONFIG_AMD_MEM_ENCRYPT=y
CONFIG_HYPERVISOR_GUEST=y
CONFIG_KVM=y
CONFIG_PARAVIRT=y

[...]

Applied to for-next/orphans, thanks!

[1/1] vmlinux.lds.h: Avoid orphan section with !SMP

      https://git.kernel.org/kees/c/d4c639990036
Signature · 1 line
Kees Cook