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    Subject[PATCH] lib/vsprintf: make-printk-non-secret printks all addresses as unhashed
    Date
    If the make-printk-non-secret command-line parameter is set, then
    printk("%p") will print addresses as unhashed. This is useful for
    debugging purposes.

    A large warning message is displayed if this option is enabled,
    because unhashed addresses, while useful for debugging, exposes
    kernel addresses which can be a security risk.

    Signed-off-by: Timur Tabi <timur@kernel.org>
    ---
    lib/vsprintf.c | 34 ++++++++++++++++++++++++++++++++--
    1 file changed, 32 insertions(+), 2 deletions(-)

    diff --git a/lib/vsprintf.c b/lib/vsprintf.c
    index 3b53c73580c5..b9f87084afb0 100644
    --- a/lib/vsprintf.c
    +++ b/lib/vsprintf.c
    @@ -2090,6 +2090,30 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
    return widen_string(buf, buf - buf_start, end, spec);
    }

    +/* Disable pointer hashing if requested */
    +static bool debug_never_hash_pointers __ro_after_init;
    +
    +static int __init debug_never_hash_pointers_enable(char *str)
    +{
    + debug_never_hash_pointers = true;
    + pr_warn("**********************************************************\n");
    + pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
    + pr_warn("** **\n");
    + pr_warn("** All pointers that are printed to the console will **\n");
    + pr_warn("** be printed as unhashed. **\n");
    + pr_warn("** **\n");
    + pr_warn("** Kernel memory addresses are exposed, which may **\n");
    + pr_warn("** compromise security on your system. **\n");
    + pr_warn("** **\n");
    + pr_warn("** If you see this message and you are not debugging **\n");
    + pr_warn("** the kernel, report this immediately to your vendor! **\n");
    + pr_warn("** **\n");
    + pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
    + pr_warn("**********************************************************\n");
    + return 0;
    +}
    +early_param("make-printk-non-secret", debug_never_hash_pointers_enable);
    +
    /*
    * Show a '%p' thing. A kernel extension is that the '%p' is followed
    * by an extra set of alphanumeric characters that are extended format
    @@ -2297,8 +2321,14 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
    }
    }

    - /* default is to _not_ leak addresses, hash before printing */
    - return ptr_to_id(buf, end, ptr, spec);
    + /*
    + * default is to _not_ leak addresses, so hash before printing, unless
    + * make-printk-non-secret is specified on the command line.
    + */
    + if (unlikely(debug_never_hash_pointers))
    + return pointer_string(buf, end, ptr, spec);
    + else
    + return ptr_to_id(buf, end, ptr, spec);
    }

    /*
    --
    2.25.1
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