linux-kernel - [PATCH] vmlinux.lds.h: Handle decrypted data section with !SMP

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Message-Id: <20210506001410.1026691-1-nathan@kernel.org>
Date:   Wed,  5 May 2021 17:14:11 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Kees Cook <keescook@...omium.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        Nathan Chancellor <nathan@...nel.org>,
        kernel test robot <lkp@...el.com>
Subject: [PATCH] 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 <lkp@...el.com>
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---

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(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 40a9c101565e..17325416e2de 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -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