linux-kernel - [PATCH RFC 25/43] x86/mm: Make the x86 GOT read-only

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Message-Id: <980069339b23a6cc4ae6d605d188338467a5b08b.1682673543.git.houwenlong.hwl@antgroup.com>
Date:   Fri, 28 Apr 2023 17:51:05 +0800
From:   "Hou Wenlong" <houwenlong.hwl@...group.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Thomas Garnier" <thgarnie@...omium.org>,
        "Lai Jiangshan" <jiangshan.ljs@...group.com>,
        "Kees Cook" <keescook@...omium.org>,
        "Hou Wenlong" <houwenlong.hwl@...group.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, "Arnd Bergmann" <arnd@...db.de>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Josh Poimboeuf" <jpoimboe@...nel.org>,
        "Juergen Gross" <jgross@...e.com>,
        "Brian Gerst" <brgerst@...il.com>, <linux-arch@...r.kernel.org>
Subject: [PATCH RFC 25/43] x86/mm: Make the x86 GOT read-only

From: Thomas Garnier <thgarnie@...omium.org>

From: Thomas Garnier <thgarnie@...omium.org>

The GOT is changed during early boot when relocations are applied. Make
it read-only directly. This table exists only for PIE binary. Since weak
symbol reference would always be GOT reference, there are 8 entries in
GOT, but only one entry for __fentry__() is in use.  Other GOT
references have been optimized by linker.

[Hou Wenlong: Change commit message and skip GOT size check]

Signed-off-by: Thomas Garnier <thgarnie@...omium.org>
Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
Cc: Lai Jiangshan <jiangshan.ljs@...group.com>
Cc: Kees Cook <keescook@...omium.org>
---
 arch/x86/kernel/vmlinux.lds.S     |  2 ++
 include/asm-generic/vmlinux.lds.h | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index f02dcde9f8a8..fa4c6582663f 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -462,6 +462,7 @@ SECTIONS
 #endif
 	       "Unexpected GOT/PLT entries detected!")
 
+#ifndef CONFIG_X86_PIE
 	/*
 	 * Sections that should stay zero sized, which is safer to
 	 * explicitly check instead of blindly discarding.
@@ -470,6 +471,7 @@ SECTIONS
 		*(.got) *(.igot.*)
 	}
 	ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
+#endif
 
 	.plt : {
 		*(.plt) *(.plt.*) *(.iplt)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index d1f57e4868ed..438ed8b39896 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -441,6 +441,17 @@
 	__end_ro_after_init = .;
 #endif
 
+#ifdef CONFIG_X86_PIE
+#define RO_GOT_X86							\
+	.got        : AT(ADDR(.got) - LOAD_OFFSET) {			\
+		__start_got = .;					\
+		*(.got) *(.igot.*);					\
+		__end_got = .;						\
+	}
+#else
+#define RO_GOT_X86
+#endif
+
 /*
  * .kcfi_traps contains a list KCFI trap locations.
  */
@@ -486,6 +497,7 @@
 		BOUNDED_SECTION_PRE_LABEL(.pci_fixup_suspend_late, _pci_fixups_suspend_late, __start, __end) \
 	}								\
 									\
+	RO_GOT_X86							\
 	FW_LOADER_BUILT_IN_DATA						\
 	TRACEDATA							\
 									\
-- 
2.31.1