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    SubjectRe: [PATCH v4 02/29] rxrpc: Avoid using stack memory in SG lists in rxkad
    Date
    Andy Lutomirski <luto@kernel.org> wrote:

    > - skcipher_request_set_crypt(req, &sg[1], &sg[0], sizeof(tmpbuf), iv.x);
    > + skcipher_request_set_crypt(req, &sg, &sg, sizeof(tmpbuf), iv.x);

    Don't the sg's have to be different? Aren't they both altered by the process
    of reading/writing from them?

    > struct rxrpc_skb_priv *sp;
    > ...
    > + swap(tmpbuf.xl, *(__be64 *)sp);
    > +
    > + sg_init_one(&sg, sp, sizeof(tmpbuf));

    ???? I assume you're assuming that the rxrpc_skb_priv struct contents can
    arbitrarily replaced temporarily...

    And using an XCHG-equivalent instruction? This won't work on a 32-bit arch
    (apart from one that sports CMPXCHG8 or similar).

    > /*
    > - * load a scatterlist with a potentially split-page buffer
    > + * load a scatterlist
    > */
    > -static void rxkad_sg_set_buf2(struct scatterlist sg[2],
    > +static void rxkad_sg_set_buf2(struct scatterlist sg[1],
    > void *buf, size_t buflen)
    > {
    > - int nsg = 1;
    > -
    > - sg_init_table(sg, 2);
    > -
    > + sg_init_table(sg, 1);
    > sg_set_buf(&sg[0], buf, buflen);
    > - if (sg[0].offset + buflen > PAGE_SIZE) {
    > - /* the buffer was split over two pages */
    > - sg[0].length = PAGE_SIZE - sg[0].offset;
    > - sg_set_buf(&sg[1], buf + sg[0].length, buflen - sg[0].length);
    > - nsg++;
    > - }
    > -
    > - sg_mark_end(&sg[nsg - 1]);
    > -
    > - ASSERTCMP(sg[0].length + sg[1].length, ==, buflen);
    > }

    This should be a separate patch.

    David

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