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| author |   Sven Schnelle <svens@linux.ibm.com> | 2021-04-07 09:20:17 +0200 |
|---|---|---|
| committer |   Vasily Gorbik <gor@linux.ibm.com> | 2021-10-26 15:21:29 +0200 |
| commit | 3b051e89da70d464a036a86d70ce2ed61c73f792 (patch) | |
| tree | ad9a4dc6ce89d26aaf92d530d48df8e992c629e6 /arch/s390/mm | |
| parent | s390: introduce nospec_uses_trampoline() (diff) | |
| download | linux-dev-3b051e89da70d464a036a86d70ce2ed61c73f792.tar.xz linux-dev-3b051e89da70d464a036a86d70ce2ed61c73f792.zip | |
s390: add support for BEAR enhancement facility
The Breaking-Event-Address-Register (BEAR) stores the address of the
last breaking event instruction. Breaking events are usually instructions
that change the program flow - for example branches, and instructions
that modify the address in the PSW like lpswe. This is useful for debugging
wild branches, because one could easily figure out where the wild branch
was originating from.
What is problematic is that lpswe is considered a breaking event, and
therefore overwrites BEAR on kernel exit. The BEAR enhancement facility
adds new instructions that allow to save/restore BEAR and also an lpswey
instruction that doesn't cause a breaking event. So we can save BEAR on
kernel entry and restore it on exit to user space.
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Diffstat (limited to 'arch/s390/mm')
| -rw-r--r-- | arch/s390/mm/dump_pagetables.c | 14 | ||||
| -rw-r--r-- | arch/s390/mm/vmem.c | 10 |
2 files changed, 19 insertions, 5 deletions
diff --git a/arch/s390/mm/dump_pagetables.c b/arch/s390/mm/dump_pagetables.c index 0b0c8c284953..9f9af5298dd6 100644 --- a/arch/s390/mm/dump_pagetables.c +++ b/arch/s390/mm/dump_pagetables.c @@ -8,6 +8,7 @@ #include <linux/kasan.h> #include <asm/ptdump.h> #include <asm/kasan.h> +#include <asm/nospec-branch.h> #include <asm/sections.h> static unsigned long max_addr; @@ -116,8 +117,13 @@ static void note_prot_wx(struct pg_state *st, unsigned long addr) return; if (st->current_prot & _PAGE_NOEXEC) return; - /* The first lowcore page is currently still W+X. */ - if (addr == PAGE_SIZE) + /* + * The first lowcore page is W+X if spectre mitigations are using + * trampolines or the BEAR enhancements facility is not installed, + * in which case we have two lpswe instructions in lowcore that need + * to be executable. + */ + if (addr == PAGE_SIZE && (nospec_uses_trampoline() || !static_key_enabled(&cpu_has_bear))) return; WARN_ONCE(1, "s390/mm: Found insecure W+X mapping at address %pS\n", (void *)st->start_address); @@ -203,7 +209,9 @@ void ptdump_check_wx(void) if (st.wx_pages) pr_warn("Checked W+X mappings: FAILED, %lu W+X pages found\n", st.wx_pages); else - pr_info("Checked W+X mappings: passed, no unexpected W+X pages found\n"); + pr_info("Checked W+X mappings: passed, no %sW+X pages found\n", + (nospec_uses_trampoline() || !static_key_enabled(&cpu_has_bear)) ? + "unexpected " : ""); } #endif /* CONFIG_DEBUG_WX */ diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c index 2b1c6d916cf9..7d9705eeb02f 100644 --- a/arch/s390/mm/vmem.c +++ b/arch/s390/mm/vmem.c @@ -13,6 +13,7 @@ #include <linux/hugetlb.h> #include <linux/slab.h> #include <asm/cacheflush.h> +#include <asm/nospec-branch.h> #include <asm/pgalloc.h> #include <asm/setup.h> #include <asm/tlbflush.h> @@ -584,8 +585,13 @@ void __init vmem_map_init(void) __set_memory(__stext_amode31, (__etext_amode31 - __stext_amode31) >> PAGE_SHIFT, SET_MEMORY_RO | SET_MEMORY_X); - /* we need lowcore executable for our LPSWE instructions */ - set_memory_x(0, 1); + if (nospec_uses_trampoline() || !static_key_enabled(&cpu_has_bear)) { + /* + * Lowcore must be executable for LPSWE + * and expoline trampoline branch instructions. + */ + set_memory_x(0, 1); + } pr_info("Write protected kernel read-only data: %luk\n", (unsigned long)(__end_rodata - _stext) >> 10); |