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| author | Alexander Gordeev <agordeev@linux.ibm.com> | 2024-08-09 08:47:16 +0200 |
|---|---|---|
| committer | Vasily Gorbik <gor@linux.ibm.com> | 2024-08-21 16:14:45 +0200 |
| commit | 32db401965f165f7c44447d0508097f070c8f576 (patch) | |
| tree | 9bcb4095ae072156c43a3ec3a60eaebbf2ba416f | |
| parent | a3ca27c405faad584af6e8e38cdafe5be73230a1 (diff) | |
| download | lwn-32db401965f165f7c44447d0508097f070c8f576.tar.gz lwn-32db401965f165f7c44447d0508097f070c8f576.zip | |
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: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
| -rw-r--r-- | arch/s390/Kconfig | 13 | ||||
| -rw-r--r-- | arch/s390/boot/startup.c | 3 |
2 files changed, 15 insertions, 1 deletions
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig index a822f952f64a..c60e699e99f5 100644 --- a/arch/s390/Kconfig +++ b/arch/s390/Kconfig @@ -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 diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c index ce232552bc1c..cff34744b5a9 100644 --- a/arch/s390/boot/startup.c +++ b/arch/s390/boot/startup.c @@ -341,7 +341,8 @@ 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; } |