[PATCH v6 14/14] arm64: hibernate: Prevent resume from a different kernel version

[James Morse]

Resuming using a different kernel version is fragile, while there are
sufficient details in the hibernate arch-header to perform the restore,
changes in the boot process can have a long-lasting impact on the system.
In particular, if the EFI stub causes more runtime services memory to be
allocated, the amount of memory left for linux is reduced. If we are
lucky, this will cause restore to fail with the message:
> PM: Image mismatch: memory size
If we are unlucky, the system will explode sometime later when an EFI
runtime services call is made.

Prevent resuming with a different kernel build, by storing UTS_VERSION
in the hibernate header. This also ensures the page size and va bits
configuration remain the same.

Signed-off-by: James Morse <james.morse at arm.com>
---
 arch/arm64/kernel/hibernate.c | 35 +++++------------------------------
 1 file changed, 5 insertions(+), 30 deletions(-)

diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c
index 279c556ee24b..486315249f2a 100644
--- a/arch/arm64/kernel/hibernate.c
+++ b/arch/arm64/kernel/hibernate.c
@@ -20,6 +20,7 @@
 #include <linux/pm.h>
 #include <linux/sched.h>
 #include <linux/suspend.h>
+#include <linux/utsname.h>
 #include <linux/version.h>
 
 #include <asm/barrier.h>
@@ -42,8 +43,6 @@
 #define pud_index(x)	0
 #endif
 
-#define TCR_IPS_BITS (0x7UL<<32)
-
 /*
  * Hibernate core relies on this value being 0 on resume, and marks it
  * __nosavedata assuming it will keep the resume kernel's '0' value. This
@@ -54,17 +53,6 @@
  */
 extern int in_suspend;
 
-/*
- * This value is written to the hibernate arch header, and prevents resuming
- * from a hibernate image produced by an incompatible kernel. If you change
- * a value that isn't saved/restored by hibernate, you should change this value.
- *
- * For example, if the mair_el1 values used by the kernel are changed, you
- * should prevent resuming from a kernel with incompatible attributes, as these
- * aren't saved/restored.
- */
-#define HIBERNATE_VERSION	KERNEL_VERSION(4, 6, 0)
-
 /* Find a symbols alias in the linear map */
 #define LMADDR(x)	phys_to_virt(virt_to_phys(x))
 
@@ -81,8 +69,7 @@ extern char hibernate_el2_vectors[];
 extern char el2_setup[];
 
 struct arch_hibernate_hdr_invariants {
-	unsigned long	version;
-	unsigned long	tcr_el1;	/* page_size, va bit etc */
+	char		uts_version[__NEW_UTS_LEN + 1];
 };
 
 /* These values need to be know across a hibernate/restore. */
@@ -104,11 +91,8 @@ static struct arch_hibernate_hdr {
 
 static inline void arch_hdr_invariants(struct arch_hibernate_hdr_invariants *i)
 {
-	i->version = HIBERNATE_VERSION;
-	asm volatile("mrs	%0, tcr_el1" : "=r"(i->tcr_el1));
-
-	/* IPS bits vary on big/little systems, mask them out */
-	i->tcr_el1 &= ~TCR_IPS_BITS;
+	memset(i, 0, sizeof(*i));
+	memcpy(i->uts_version, init_utsname()->version, sizeof(i->uts_version));
 }
 
 int pfn_is_nosave(unsigned long pfn)
@@ -155,18 +139,9 @@ int arch_hibernation_header_restore(void *addr)
 	struct arch_hibernate_hdr_invariants invariants;
 	struct arch_hibernate_hdr *hdr = addr;
 
-	/*
-	 * If this header is ancient, it may be smaller than we expect.
-	 * Test the version first.
-	 */
-	if (hdr->invariants.version != HIBERNATE_VERSION) {
-		pr_crit("Hibernate image not compatible with this kernel version!\n");
-		return -EINVAL;
-	}
-
 	arch_hdr_invariants(&invariants);
 	if (memcmp(&hdr->invariants, &invariants, sizeof(invariants))) {
-		pr_crit("Hibernate image not compatible with this kernel configuration!\n");
+		pr_crit("Hibernate image not generated by this kernel!\n");
 		return -EINVAL;
 	}
 
-- 
2.7.0