From 0b38b5e1d0e2f361e418e05c179db05bb688bbd6 Mon Sep 17 00:00:00 2001 From: Sven Schnelle Date: Wed, 22 Jan 2020 13:38:22 +0100 Subject: s390: prevent leaking kernel address in BEAR When userspace executes a syscall or gets interrupted, BEAR contains a kernel address when returning to userspace. This make it pretty easy to figure out where the kernel is mapped even with KASLR enabled. To fix this, add lpswe to lowcore and always execute it there, so userspace sees only the lowcore address of lpswe. For this we have to extend both critical_cleanup and the SWITCH_ASYNC macro to also check for lpswe addresses in lowcore. Fixes: b2d24b97b2a9 ("s390/kernel: add support for kernel address space layout randomization (KASLR)") Cc: # v5.2+ Reviewed-by: Gerald Schaefer Signed-off-by: Sven Schnelle Signed-off-by: Vasily Gorbik --- arch/s390/mm/vmem.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch/s390/mm') diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c index b403fa14847d..f810930aff42 100644 --- a/arch/s390/mm/vmem.c +++ b/arch/s390/mm/vmem.c @@ -415,6 +415,10 @@ void __init vmem_map_init(void) SET_MEMORY_RO | SET_MEMORY_X); __set_memory(__stext_dma, (__etext_dma - __stext_dma) >> PAGE_SHIFT, SET_MEMORY_RO | SET_MEMORY_X); + + /* we need lowcore executable for our LPSWE instructions */ + set_memory_x(0, 1); + pr_info("Write protected kernel read-only data: %luk\n", (unsigned long)(__end_rodata - _stext) >> 10); } -- cgit