[PATCH v2 15/29] x86: Actually use _etext for end of text segment

Kees Cook
2019-10-11T00:05:55Z

Various calculations are using the end of the exception table (which
does not need to be executable) as the end of the text segment. Instead,
in preparation for moving the exception table into RO_DATA, move _etext
after the exception table and update the calculations.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/x86/include/asm/sections.h | 1 -
arch/x86/kernel/vmlinux.lds.S | 7 +++----
arch/x86/mm/init_64.c | 6 +++---
arch/x86/mm/pti.c | 2 +-
4 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
index 71b32f2570ab..036c360910c5 100644
--- a/arch/x86/include/asm/sections.h
+++ b/arch/x86/include/asm/sections.h
@@ -6,7 +6,6 @@
#include <asm/extable.h>

extern char __brk_base[], __brk_limit[];
-extern struct exception_table_entry __stop___ex_table[];
extern char __end_rodata_aligned[];

#if defined(CONFIG_X86_64)
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 41362e90142d..a1a758e25b2b 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -143,15 +143,14 @@ SECTIONS
*(.text.__x86.indirect_thunk)
__indirect_thunk_end = .;
#endif
-
- /* End of text section */
- _etext = .;
} :text = 0x9090

EXCEPTION_TABLE(16)

- /* .text should occupy whole number of pages */
+ /* End of text section, which should occupy whole number of pages */
+ _etext = .;
. = ALIGN(PAGE_SIZE);
+
X86_ALIGN_RODATA_BEGIN
RO_DATA(PAGE_SIZE)
X86_ALIGN_RODATA_END
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index a6b5c653727b..26299e9ce6da 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1263,7 +1263,7 @@ int kernel_set_to_readonly;
void set_kernel_text_rw(void)
{
unsigned long start = PFN_ALIGN(_text);
- unsigned long end = PFN_ALIGN(__stop___ex_table);
+ unsigned long end = PFN_ALIGN(_etext);

if (!kernel_set_to_readonly)
return;
@@ -1282,7 +1282,7 @@ void set_kernel_text_rw(void)
void set_kernel_text_ro(void)
{
unsigned long start = PFN_ALIGN(_text);
- unsigned long end = PFN_ALIGN(__stop___ex_table);
+ unsigned long end = PFN_ALIGN(_etext);

if (!kernel_set_to_readonly)
return;
@@ -1301,7 +1301,7 @@ void mark_rodata_ro(void)
unsigned long start = PFN_ALIGN(_text);
unsigned long rodata_start = PFN_ALIGN(__start_rodata);
unsigned long end = (unsigned long) &__end_rodata_hpage_align;
- unsigned long text_end = PFN_ALIGN(&__stop___ex_table);
+ unsigned long text_end = PFN_ALIGN(&_etext);
unsigned long rodata_end = PFN_ALIGN(&__end_rodata);
unsigned long all_end;

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 7f2140414440..44a9f068eee0 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -574,7 +574,7 @@ static void pti_clone_kernel_text(void)
*/
unsigned long start = PFN_ALIGN(_text);
unsigned long end_clone = (unsigned long)__end_rodata_aligned;
- unsigned long end_global = PFN_ALIGN((unsigned long)__stop___ex_table);
+ unsigned long end_global = PFN_ALIGN((unsigned long)_etext);

if (!pti_kernel_image_global_ok())
return;
--
2.17.1