linux-kernel - [PATCH v3 17/19] x86/sev: Use PIC codegen for early SEV startup code

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Date: Mon, 29 Jan 2024 19:05:20 +0100
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>, Kevin Loughlin <kevinloughlin@...gle.com>, 
	Tom Lendacky <thomas.lendacky@....com>, Dionna Glaze <dionnaglaze@...gle.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>, linux-arch@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: [PATCH v3 17/19] x86/sev: Use PIC codegen for early SEV startup code

From: Ard Biesheuvel <ardb@...nel.org>

Use PIC codegen for the compilation units containing code that may be
called very early during the boot, at which point the CPU still runs
from the 1:1 mapping of memory. This is necessary to prevent the
compiler from emitting absolute symbol references to addresses that are
not mapped yet.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/kernel/Makefile      | 2 ++
 arch/x86/kernel/vmlinux.lds.S | 1 +
 arch/x86/mm/Makefile          | 2 +-
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 42db41b04d8e..3819b65c64ec 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -24,7 +24,9 @@ endif
 # head64.c contains C code that may execute from a different virtual address
 # than it was linked at, so we always build it using PIE codegen
 CFLAGS_head64.o += $(PIE_CFLAGS)
+CFLAGS_sev.o += $(PIE_CFLAGS)
 UBSAN_SANITIZE_head64.o					:= n
+UBSAN_SANITIZE_sev.o					:= n
 
 KASAN_SANITIZE_head$(BITS).o				:= n
 KASAN_SANITIZE_dumpstack.o				:= n
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 77262e804250..bbdccb6362a9 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -182,6 +182,7 @@ SECTIONS
 
 		DATA_DATA
 		CONSTRUCTORS
+		*(.data.rel .data.rel.*)
 
 		/* rarely changed data like cpu maps */
 		READ_MOSTLY_DATA(INTERNODE_CACHE_BYTES)
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index c80febc44cd2..f3bb8b415348 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -31,7 +31,7 @@ obj-y				+= pat/
 
 # Make sure __phys_addr has no stackprotector
 CFLAGS_physaddr.o		:= -fno-stack-protector
-CFLAGS_mem_encrypt_identity.o	:= -fno-stack-protector
+CFLAGS_mem_encrypt_identity.o	:= $(PIE_CFLAGS)
 
 CFLAGS_fault.o := -I $(srctree)/$(src)/../include/asm/trace
 
-- 
2.43.0.429.g432eaa2c6b-goog