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Date: Sat, 13 Nov 2021 07:40:35 -0500
From: Brian Gerst <brgerst@...il.com>
To: linux-kernel@...r.kernel.org, x86@...nel.org
Cc: Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>,
Thomas Gleixner <tglx@...utronix.de>,
"H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
Brian Gerst <brgerst@...il.com>
Subject: [PATCH 3/3] x86_64: Use relative per-cpu offsets
The per-cpu section is currently linked at virtual address 0, because
older compilers hardcoded the stack protector canary value at a fixed
offset from the start of the GS segment. Use a standard relative offset
as the GS base when the stack protector is disabled, or a newer compiler
is used that supports a configurable location for the stack canary.
Signed-off-by: Brian Gerst <brgerst@...il.com>
---
arch/x86/Kconfig | 2 +-
arch/x86/include/asm/percpu.h | 4 ++--
arch/x86/kernel/head_64.S | 4 ----
arch/x86/kernel/setup_percpu.c | 2 +-
arch/x86/kernel/vmlinux.lds.S | 14 ++++++--------
5 files changed, 10 insertions(+), 16 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 832a6626df72..fae7724505bd 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -403,7 +403,7 @@ config STACKPROTECTOR_FIXED
default y if !$(cc-option,-mstack-protector-guard-reg=gs)
config X86_ABSOLUTE_PERCPU
- def_bool X86_64 && SMP
+ def_bool STACKPROTECTOR_FIXED && SMP
select KALLSYMS_ABSOLUTE_PERCPU
menu "Processor type and features"
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index a3c33b79fb86..8294781bb483 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -16,7 +16,7 @@
#define PER_CPU_VAR(var) var
#endif /* SMP */
-#ifdef CONFIG_X86_64_SMP
+#ifdef CONFIG_X86_ABSOLUTE_PERCPU
#define INIT_PER_CPU_VAR(var) init_per_cpu__##var
#else
#define INIT_PER_CPU_VAR(var) var
@@ -59,7 +59,7 @@
#define DECLARE_INIT_PER_CPU(var) \
extern typeof(var) init_per_cpu_var(var)
-#ifdef CONFIG_X86_64_SMP
+#ifdef CONFIG_X86_ABSOLUTE_PERCPU
#define init_per_cpu_var(var) init_per_cpu__##var
#else
#define init_per_cpu_var(var) var
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 6e396ffb1610..c1b6209a01ca 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -339,12 +339,8 @@ SYM_DATA(initial_code, .quad x86_64_start_kernel)
#ifdef CONFIG_STACKPROTECTOR_FIXED
SYM_DATA(initial_gs, .quad INIT_PER_CPU_VAR(fixed_percpu_data))
#else
-#ifdef CONFIG_SMP
-SYM_DATA(initial_gs, .quad __per_cpu_load)
-#else
SYM_DATA(initial_gs, .quad 0)
#endif
-#endif
#ifdef CONFIG_AMD_MEM_ENCRYPT
SYM_DATA(initial_vc_handler, .quad handle_vc_boot_ghcb)
diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index 5afd98559193..4c0020a6ced9 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -26,7 +26,7 @@
DEFINE_PER_CPU_READ_MOSTLY(int, cpu_number);
EXPORT_PER_CPU_SYMBOL(cpu_number);
-#ifdef CONFIG_X86_64
+#ifdef CONFIG_X86_ABSOLUTE_PERCPU
#define BOOT_PERCPU_OFFSET ((unsigned long)__per_cpu_load)
#else
#define BOOT_PERCPU_OFFSET 0
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index c475d21d2126..18e1deb9fa52 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -102,10 +102,10 @@ jiffies = jiffies_64;
PHDRS {
text PT_LOAD FLAGS(5); /* R_E */
data PT_LOAD FLAGS(6); /* RW_ */
-#ifdef CONFIG_X86_64
-#ifdef CONFIG_SMP
+#ifdef CONFIG_X86_ABSOLUTE_PERCPU
percpu PT_LOAD FLAGS(6); /* RW_ */
#endif
+#ifdef CONFIG_X86_64
init PT_LOAD FLAGS(7); /* RWE */
#endif
note PT_NOTE FLAGS(0); /* ___ */
@@ -215,7 +215,7 @@ SECTIONS
__init_begin = .; /* paired with __init_end */
}
-#if defined(CONFIG_X86_64) && defined(CONFIG_SMP)
+#ifdef CONFIG_X86_ABSOLUTE_PERCPU
/*
* percpu offsets are zero-based on SMP. PERCPU_VADDR() changes the
* output PHDR, so the next output section - .init.text - should
@@ -339,7 +339,7 @@ SECTIONS
EXIT_DATA
}
-#if !defined(CONFIG_X86_64) || !defined(CONFIG_SMP)
+#ifndef CONFIG_X86_ABSOLUTE_PERCPU
PERCPU_SECTION(INTERNODE_CACHE_BYTES)
#endif
@@ -474,7 +474,7 @@ SECTIONS
. = ASSERT((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),
"kernel image bigger than KERNEL_IMAGE_SIZE");
-#ifdef CONFIG_X86_64
+#ifdef CONFIG_X86_ABSOLUTE_PERCPU
/*
* Per-cpu symbols which need to be offset from __per_cpu_load
* for the boot processor.
@@ -483,13 +483,11 @@ SECTIONS
INIT_PER_CPU(gdt_page);
INIT_PER_CPU(irq_stack_backing_store);
-#ifdef CONFIG_STACKPROTECTOR_FIXED
INIT_PER_CPU(fixed_percpu_data);
. = ASSERT((fixed_percpu_data == 0),
"fixed_percpu_data is not at start of per-cpu area");
-#endif
-#endif /* CONFIG_X86_64 */
+#endif /* CONFIG_X86_ABSOLUTE_PERCPU */
#ifdef CONFIG_KEXEC_CORE
#include <asm/kexec.h>
--
2.31.1
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