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

[Pavel Machek]

On Mon 2016-02-29 17:20:23, James Morse wrote:
> 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>

Better solution would be to store the current bits _and_ UTS version. Then bump UTS_VERSION
every time Linux behaviour changes w.r.t. EFI. For a while, it would change a lot, but then
it should stabilize, as the port stabilizes


> ---
>  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

-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html