For security hardening reasons, it advantageous to make setup-once data
immutable after boot. Borrow __ro_after_init from Linux.
On x86, place .data.ro_after_init at the start of .rodata, excluding it from
the early permission restrictions. Re-apply RO restrictions to the whole of
.rodata in init_done(), attempting to reform the superpage if possible.
For architectures which don't implement __ro_after_init explicitly, variables
merges into .data.
Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
---
CC: Jan Beulich <jbeul...@suse.com>
CC: Roger Pau Monné <roger....@citrix.com>
CC: Wei Liu <w...@xen.org>
---
xen/arch/x86/setup.c | 12 +++++++++++-
xen/arch/x86/xen.lds.S | 6 ++++++
xen/include/asm-x86/setup.h | 1 +
xen/include/xen/cache.h | 2 ++
4 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 8329263430ed..3bbc46f244b9 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -663,6 +663,11 @@ static void noreturn init_done(void)
init_xenheap_pages(__pa(start), __pa(end));
printk("Freed %lukB init memory\n", (end - start) >> 10);
+ /* Mark .rodata/ro_after_init as RO. Maybe reform the superpage. */
+ modify_xen_mappings((unsigned long)&__2M_rodata_start,
+ (unsigned long)&__2M_rodata_end,
+ PAGE_HYPERVISOR_RO);
+
startup_cpu_idle_loop();
}
@@ -1541,8 +1546,13 @@ void __init noreturn __start_xen(unsigned long mbi_p)
(unsigned long)&__2M_text_end,
PAGE_HYPERVISOR_RX);
+ /* Mark .data.ro_after_init as RW. Maybe shatters the .rodata superpage.
*/
+ modify_xen_mappings((unsigned long)&__ro_after_init_start,
+ (unsigned long)&__ro_after_init_end,
+ PAGE_HYPERVISOR_RW);
+
/* Mark .rodata as RO. */
- modify_xen_mappings((unsigned long)&__2M_rodata_start,
+ modify_xen_mappings((unsigned long)&__ro_after_init_end,
(unsigned long)&__2M_rodata_end,
PAGE_HYPERVISOR_RO);
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 87e344d4dd97..4db5b404e073 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -97,6 +97,12 @@ SECTIONS
__2M_rodata_start = .; /* Start of 2M superpages, mapped RO. */
DECL_SECTION(.rodata) {
_srodata = .;
+
+ __ro_after_init_start = .;
+ *(.data.ro_after_init)
+ . = ALIGN(PAGE_SIZE);
+ __ro_after_init_end = .;
+
/* Bug frames table */
__start_bug_frames = .;
*(.bug_frames.0)
diff --git a/xen/include/asm-x86/setup.h b/xen/include/asm-x86/setup.h
index eb9d7b433c13..34edea405f85 100644
--- a/xen/include/asm-x86/setup.h
+++ b/xen/include/asm-x86/setup.h
@@ -6,6 +6,7 @@
extern const char __2M_text_start[], __2M_text_end[];
extern const char __2M_rodata_start[], __2M_rodata_end[];
+extern const char __ro_after_init_start[], __ro_after_init_end[];
extern char __2M_init_start[], __2M_init_end[];
extern char __2M_rwdata_start[], __2M_rwdata_end[];
diff --git a/xen/include/xen/cache.h b/xen/include/xen/cache.h
index 6ee174efa439..f52a0aedf768 100644
--- a/xen/include/xen/cache.h
+++ b/xen/include/xen/cache.h
@@ -15,4 +15,6 @@
#define __cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES)))
#endif
+#define __ro_after_init __section(".data.ro_after_init")
+
#endif /* __LINUX_CACHE_H */
--
2.11.0
