Messages in this thread | | | Subject | Re: [PATCH 3/4] arm64/kprobes: set VM_FLUSH_RESET_PERMS on kprobe instruction pages | From | Anshuman Khandual <> | Date | Tue, 28 May 2019 13:50:36 +0530 |
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On 05/23/2019 03:52 PM, Ard Biesheuvel wrote: > In order to avoid transient inconsistencies where freed code pages > are remapped writable while stale TLB entries still exist on other > cores, mark the kprobes text pages with the VM_FLUSH_RESET_PERMS > attribute. This instructs the core vmalloc code not to defer the > TLB flush when this region is unmapped and returned to the page > allocator.
Makes sense.
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com> > --- > arch/arm64/kernel/probes/kprobes.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c > index 2509fcb6d404..036cfbf9682a 100644 > --- a/arch/arm64/kernel/probes/kprobes.c > +++ b/arch/arm64/kernel/probes/kprobes.c > @@ -131,8 +131,10 @@ void *alloc_insn_page(void) > void *page; > > page = vmalloc_exec(PAGE_SIZE); > - if (page) > + if (page) { > set_memory_ro((unsigned long)page, 1); > + set_vm_flush_reset_perms(page); > + }
Looks good. It seems there might be more users who would like to set VM_FLUSH_RESET_PERMS right after their allocation for the same reason. Hence would not it help to have a variant like vmalloc_exec_reset() or such which will tag vm_struct->flags with VM_FLUSH_RESET_PERMS right after it's allocation without requiring the caller to do the same.
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