Commit 32db4019 authored by Alexander Gordeev's avatar Alexander Gordeev Committed by Vasily Gorbik
Browse files

s390/mm: Pin identity mapping base to zero 



SIE instruction performs faster when the virtual address of
SIE block matches the physical one. Pin the identity mapping
base to zero for the benefit of SIE and other instructions
that have similar performance impact. Still, randomize the
base when DEBUG_VM kernel configuration option is enabled.

Suggested-by: default avatarVasily Gorbik <gor@linux.ibm.com>
Reviewed-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
parent a3ca27c4

arch/s390/Kconfig

+13 −0
Original line number Diff line number Diff line
@@ -604,6 +604,19 @@ config RANDOMIZE_BASE 
	  as a security feature that deters exploit attempts relying on

	  knowledge of the location of kernel internals.



config RANDOMIZE_IDENTITY_BASE

	bool "Randomize the address of the identity mapping base"

	depends on RANDOMIZE_BASE

	default DEBUG_VM

	help

	  The identity mapping base address is pinned to zero by default.

	  Allow randomization of that base to expose otherwise missed

	  notion of physical and virtual addresses of data structures.

	  That does not have any impact on the base address at which the

	  kernel image is loaded.



	  If unsure, say N



config KERNEL_IMAGE_BASE

	hex "Kernel image base address"

	range 0x100000 0x1FFFFFE0000000 if !KASAN

arch/s390/boot/startup.c

+2 −1
Original line number Diff line number Diff line
@@ -341,6 +341,7 @@ static unsigned long setup_kernel_memory_layout(unsigned long kernel_size) 
	BUILD_BUG_ON(MAX_DCSS_ADDR > (1UL << MAX_PHYSMEM_BITS));

	max_mappable = max(ident_map_size, MAX_DCSS_ADDR);

	max_mappable = min(max_mappable, vmemmap_start);

	if (IS_ENABLED(CONFIG_RANDOMIZE_IDENTITY_BASE))

		__identity_base = round_down(vmemmap_start - max_mappable, rte_size);



	return asce_limit;