On Thu, 8 Mar 2018 22:18:12 -0500
Francis Deslauriers <francis.deslauri...@efficios.com> wrote:
> .entry_trampoline is a code area that is used to ensure page table
> isolation between userspace and kernelspace.
>
> At the beginning of the execution of the trampoline, we load the
> kernel's CR3 register. This has the effect of enabling the translation
> of the kernel virtual addresses to physical addresses. Before this
> happens most kernel addresses can not be translated because the running
> process' CR3 is still used.
>
> If a kprobe is placed on the trampoline code before that change of the
> CR3 register happens the kernel crashes because int3 handling pages are
> not accessible.
>
> To fix this, add the .entry_trampoline section to the kprobe blacklist
> to prohibit the probing of code before all the kernel pages are
> accessible.
OK, looks good to me.
Acked-by: Masami Hiramatsu <mhira...@kernel.org>
Ingo, could you pick it as an urgent fix?
Thanks!
>
> Signed-off-by: Francis Deslauriers <francis.deslauri...@efficios.com>
> ---
> arch/x86/include/asm/sections.h | 1 +
> arch/x86/kernel/kprobes/core.c | 10 +++++++++-
> arch/x86/kernel/vmlinux.lds.S | 2 ++
> 3 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
> index d6baf23..5c019d2 100644
> --- a/arch/x86/include/asm/sections.h
> +++ b/arch/x86/include/asm/sections.h
> @@ -10,6 +10,7 @@ extern struct exception_table_entry __stop___ex_table[];
>
> #if defined(CONFIG_X86_64)
> extern char __end_rodata_hpage_align[];
> +extern char __entry_trampoline_start[], __entry_trampoline_end[];
> #endif
>
> #endif /* _ASM_X86_SECTIONS_H */
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index bd36f3c..0715f82 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -1168,10 +1168,18 @@ NOKPROBE_SYMBOL(longjmp_break_handler);
>
> bool arch_within_kprobe_blacklist(unsigned long addr)
> {
> + bool is_in_entry_trampoline_section = false;
> +
> +#ifdef CONFIG_X86_64
> + is_in_entry_trampoline_section =
> + (addr >= (unsigned long)__entry_trampoline_start &&
> + addr < (unsigned long)__entry_trampoline_end);
> +#endif
> return (addr >= (unsigned long)__kprobes_text_start &&
> addr < (unsigned long)__kprobes_text_end) ||
> (addr >= (unsigned long)__entry_text_start &&
> - addr < (unsigned long)__entry_text_end);
> + addr < (unsigned long)__entry_text_end) ||
> + is_in_entry_trampoline_section;
> }
>
> int __init arch_init_kprobes(void)
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index 9b138a0..b854ebf 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -118,9 +118,11 @@ SECTIONS
>
> #ifdef CONFIG_X86_64
> . = ALIGN(PAGE_SIZE);
> + VMLINUX_SYMBOL(__entry_trampoline_start) = .;
> _entry_trampoline = .;
> *(.entry_trampoline)
> . = ALIGN(PAGE_SIZE);
> + VMLINUX_SYMBOL(__entry_trampoline_end) = .;
> ASSERT(. - _entry_trampoline == PAGE_SIZE, "entry trampoline is
> too big");
> #endif
>
> --
> 2.7.4
>
--
Masami Hiramatsu <mhira...@kernel.org>
