6.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Alexander Gordeev <agordeev@xxxxxxxxxxxxx> [ Upstream commit 32db401965f165f7c44447d0508097f070c8f576 ] 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: Vasily Gorbik <gor@xxxxxxxxxxxxx> Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx> Signed-off-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx> Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- arch/s390/Kconfig | 13 +++++++++++++ arch/s390/boot/startup.c | 3 ++- 2 files changed, 15 insertions(+), 1 deletion(-) diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig index c59d2b54df49..4f7ed0cd12cc 100644 --- a/arch/s390/Kconfig +++ b/arch/s390/Kconfig @@ -602,6 +602,19 @@ 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 diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c index 66ee97ac803d..90c51368f933 100644 --- a/arch/s390/boot/startup.c +++ b/arch/s390/boot/startup.c @@ -333,7 +333,8 @@ 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); - __identity_base = round_down(vmemmap_start - max_mappable, rte_size); + if (IS_ENABLED(CONFIG_RANDOMIZE_IDENTITY_BASE)) + __identity_base = round_down(vmemmap_start - max_mappable, rte_size); return asce_limit; } -- 2.43.0
