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    SubjectRe: [PATCH 0/2] introduce DUMP_PREFIX_UNHASHED for hex dumps
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    On 1/19/21 1:45 PM, Kees Cook wrote:
    > How about this so the base address is hashed once, with the offset added
    > to it for each line instead of each line having a "new" hash that makes
    > no sense:
    >
    > diff --git a/lib/hexdump.c b/lib/hexdump.c
    > index 9301578f98e8..20264828752d 100644
    > --- a/lib/hexdump.c
    > +++ b/lib/hexdump.c
    > @@ -242,12 +242,17 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
    > const void *buf, size_t len, bool ascii)
    > {
    > const u8 *ptr = buf;
    > + const u8 *addr;
    > int i, linelen, remaining = len;
    > unsigned char linebuf[32 * 3 + 2 + 32 + 1];
    >
    > if (rowsize != 16 && rowsize != 32)
    > rowsize = 16;
    >
    > + if (prefix_type == DUMP_PREFIX_ADDRESS &&
    > + ptr_to_hashval(ptr, &addr))
    > + addr = 0;
    > +
    > for (i = 0; i < len; i += rowsize) {
    > linelen = min(remaining, rowsize);
    > remaining -= rowsize;
    > @@ -258,7 +263,7 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
    > switch (prefix_type) {
    > case DUMP_PREFIX_ADDRESS:
    > printk("%s%s%p: %s\n",
    > - level, prefix_str, ptr + i, linebuf);
    > + level, prefix_str, addr + i, linebuf);

    Well, this is better than nothing, but not by much. Again, as long as
    %px exists for printk(), I just cannot understand any resistance to
    allowing it in print_hex_dump().

    Frankly, I think this patch and my patch should both be added. During
    debugging, it's very difficult if not impossible to work with hashed
    addresses. I use print_hex_dump() with an unhashed address all the
    time, either by applying my patch to my own kernel or just replacing the
    %p with %px.

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