linux-kernel - [RFC PATCH 06/11] x86: make sure _etext includes function sections

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Message-Id: <20200205223950.1212394-7-kristen@linux.intel.com>
Date:   Wed,  5 Feb 2020 14:39:45 -0800
From:   Kristen Carlson Accardi <kristen@...ux.intel.com>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        arjan@...ux.intel.com, keescook@...omium.org
Cc:     rick.p.edgecombe@...el.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        Kristen Carlson Accardi <kristen@...ux.intel.com>
Subject: [RFC PATCH 06/11] x86: make sure _etext includes function sections

We will be using -ffunction-sections to place each function in
it's own text section so it can be randomized at load time. The
linker considers these .text.* sections "orphaned sections", and
will place them after the first similar section (.text). However,
we need to move _etext so that it is after both .text and .text.*
We also need to calculate text size to include .text AND .text.*

Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
---
 arch/x86/kernel/vmlinux.lds.S     | 18 +++++++++++++++++-
 include/asm-generic/vmlinux.lds.h |  2 +-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 3a1a819da137..e54e9ac5b429 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -146,8 +146,24 @@ SECTIONS
 #endif
 	} :text =0xcccc
 
-	/* End of text section, which should occupy whole number of pages */
+#ifdef CONFIG_FG_KASLR
+	/*
+	 * -ffunction-sections creates .text.* sections, which are considered
+	 * "orphan sections" and added after the first similar section (.text).
+	 * Adding this ALIGN statement causes the address of _etext
+	 * to be below that of all the .text.* orphaned sections
+	 */
+	. = ALIGN(PAGE_SIZE);
+#endif
 	_etext = .;
+
+	/*
+	 * the size of the .text section is used to calculate the address
+	 * range for orc lookups. If we just use SIZEOF(.text), we will
+	 * miss all the .text.* sections. Calculate the size using _etext
+	 * and _stext and save the value for later.
+	 */
+	text_size = _etext - _stext;
 	. = ALIGN(PAGE_SIZE);
 
 	X86_ALIGN_RODATA_BEGIN
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index e00f41aa8ec4..edf19f4296e2 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -798,7 +798,7 @@
 	. = ALIGN(4);							\
 	.orc_lookup : AT(ADDR(.orc_lookup) - LOAD_OFFSET) {		\
 		orc_lookup = .;						\
-		. += (((SIZEOF(.text) + LOOKUP_BLOCK_SIZE - 1) /	\
+		. += (((text_size + LOOKUP_BLOCK_SIZE - 1) /	\
 			LOOKUP_BLOCK_SIZE) + 1) * 4;			\
 		orc_lookup_end = .;					\
 	}
-- 
2.24.1