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    SubjectRe: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier usages
    On (09/07/17 16:56), Sergey Senozhatsky wrote:
    [..]
    > BTW, are we sure we can crash? when attempt to deference IP from
    > the given descriptor? shall we handle page fault in this case and
    > do something sane? just asking.

    I don't know... does the below code make any sense?

    quick and dirty. NOT TESTED at all (not even compile tested).
    we can avoid extra probe_kernel_address() on anything that is
    not ia64, ppc64, etc.

    basically it checks that it's safe to access ptr (we can access it
    without page fault in __dereference_function_descriptor()). then
    we do ptr->ip, and also check if it's safe, but in
    dereference_function_descriptor().

    I suppose somethign like

    pr_err("%pF\n", 1);

    can crash ia64, etc. correct?


    well. not tested.

    ---

    lib/vsprintf.c | 12 +++++++++++-
    1 file changed, 11 insertions(+), 1 deletion(-)

    diff --git a/lib/vsprintf.c b/lib/vsprintf.c
    index 86c3385b9eb3..0dc39b95e1d9 100644
    --- a/lib/vsprintf.c
    +++ b/lib/vsprintf.c
    @@ -1593,6 +1593,16 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,

    int kptr_restrict __read_mostly;

    +static void *__dereference_function_descriptor(void *ptr)
    +{
    + void *p;
    +
    + if (!probe_kernel_address(ptr, p))
    + return dereference_function_descriptor(ptr);
    +
    + return ptr;
    +}
    +
    /*
    * Show a '%p' thing. A kernel extension is that the '%p' is followed
    * by an extra set of alphanumeric characters that are extended format
    @@ -1723,7 +1733,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
    switch (*fmt) {
    case 'F':
    case 'f':
    - ptr = dereference_function_descriptor(ptr);
    + ptr = __dereference_function_descriptor(ptr);
    /* Fallthrough */
    case 'S':
    case 's':

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