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    Subject[PATCH 4.9 012/102] kprobes/x86: Fix to set RWX bits correctly before releasing trampoline
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Masami Hiramatsu <mhiramat@kernel.org>

    commit c93f5cf571e7795f97d49ef51b766cf25e328545 upstream.

    Fix kprobes to set(recover) RWX bits correctly on trampoline
    buffer before releasing it. Releasing readonly page to
    module_memfree() crash the kernel.

    Without this fix, if kprobes user register a bunch of kprobes
    in function body (since kprobes on function entry usually
    use ftrace) and unregister it, kernel hits a BUG and crash.

    Link: http://lkml.kernel.org/r/149570868652.3518.14120169373590420503.stgit@devbox

    Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
    Fixes: d0381c81c2f7 ("kprobes/x86: Set kprobes pages read-only")
    Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    Cc: Ben Hutchings <ben.hutchings@codethink.co.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/kernel/kprobes/core.c | 9 +++++++++
    kernel/kprobes.c | 2 +-
    2 files changed, 10 insertions(+), 1 deletion(-)

    --- a/arch/x86/kernel/kprobes/core.c
    +++ b/arch/x86/kernel/kprobes/core.c
    @@ -51,6 +51,7 @@
    #include <linux/ftrace.h>
    #include <linux/frame.h>
    #include <linux/kasan.h>
    +#include <linux/moduleloader.h>

    #include <asm/text-patching.h>
    #include <asm/cacheflush.h>
    @@ -405,6 +406,14 @@ int __copy_instruction(u8 *dest, u8 *src
    return length;
    }

    +/* Recover page to RW mode before releasing it */
    +void free_insn_page(void *page)
    +{
    + set_memory_nx((unsigned long)page & PAGE_MASK, 1);
    + set_memory_rw((unsigned long)page & PAGE_MASK, 1);
    + module_memfree(page);
    +}
    +
    static int arch_copy_kprobe(struct kprobe *p)
    {
    int ret;
    --- a/kernel/kprobes.c
    +++ b/kernel/kprobes.c
    @@ -125,7 +125,7 @@ static void *alloc_insn_page(void)
    return module_alloc(PAGE_SIZE);
    }

    -static void free_insn_page(void *page)
    +void __weak free_insn_page(void *page)
    {
    module_memfree(page);
    }

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