[v3,05/10] x86: Make sure _etext includes function sections

Commit Message

Kristen Carlson Accardi June 23, 2020, 5:23 p.m. UTC

When 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). In order
to accurately represent the end of the text section and the
orphaned sections, _etext must be moved so that it is after both
.text and .text.* The text size must also be calculated to
include .text AND .text.*

Signed-off-by: Kristen Carlson Accardi <[e-mail]>
Reviewed-by: Tony Luck <[e-mail]>
Tested-by: Tony Luck <[e-mail]>
---
 arch/x86/kernel/vmlinux.lds.S     | 17 +++++++++++++++--
 include/asm-generic/vmlinux.lds.h |  2 +-
 2 files changed, 16 insertions(+), 3 deletions(-)

Comments

Kees Cook June 24, 2020, 4:52 a.m. UTC | #1

On Tue, Jun 23, 2020 at 10:23:22AM -0700, Kristen Carlson Accardi wrote:
> When 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). In order
> to accurately represent the end of the text section and the
> orphaned sections, _etext must be moved so that it is after both
> .text and .text.* The text size must also be calculated to
> include .text AND .text.*
> 
> Signed-off-by: Kristen Carlson Accardi <[e-mail]>

Reviewed-by: Kees Cook <[e-mail]>

Patch

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 3bfc8dd8a43d..e8da7eeb4d8d 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -146,9 +146,22 @@  SECTIONS
 #endif
 	} :text =0xcccc
 
-	/* End of text section, which should occupy whole number of pages */
-	_etext = .;
+	/*
+	 * -ffunction-sections creates .text.* sections, which are considered
+	 * "orphan sections" and added after the first similar section (.text).
+	 * Placing this ALIGN statement before _etext causes the address of
+	 * _etext to be below that of all the .text.* orphaned sections
+	 */
 	. = ALIGN(PAGE_SIZE);
+	_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;
 
 	X86_ALIGN_RODATA_BEGIN
 	RO_DATA(PAGE_SIZE)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index a5552cf28d5d..34eab6513fdc 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -835,7 +835,7 @@ 
 	. = 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 = .;					\
 	}