linux-kernel - Re: [PATCH] crypto: testmgr - allocate buffers with __GFP

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Date:   Thu, 11 Apr 2019 13:32:32 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Eric Biggers <ebiggers@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Matthew Wilcox <willy@...radead.org>
Cc:     linux-crypto <linux-crypto@...r.kernel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Kees Cook <keescook@...omium.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Laura Abbott <labbott@...hat.com>
Subject: Re: [PATCH] crypto: testmgr - allocate buffers with __GFP_COMP

On Thu, Apr 11, 2019 at 12:31 PM Eric Biggers <ebiggers@...nel.org> wrote:
>
> From: Eric Biggers <ebiggers@...gle.com>
>
> This is needed so that CONFIG_HARDENED_USERCOPY_PAGESPAN=y doesn't
> incorrectly report a buffer overflow when the destination of
> copy_from_iter() spans the page boundary in the 2-page buffer.
>
> Fixes: 3f47a03df6e8 ("crypto: testmgr - add testvec_config struct and helper functions")
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

> ---
>  crypto/testmgr.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/crypto/testmgr.c b/crypto/testmgr.c
> index 0f6bfb6ce6a46..3522c0bed2492 100644
> --- a/crypto/testmgr.c
> +++ b/crypto/testmgr.c
> @@ -156,7 +156,8 @@ static int __testmgr_alloc_buf(char *buf[XBUFSIZE], int order)
>         int i;
>
>         for (i = 0; i < XBUFSIZE; i++) {
> -               buf[i] = (char *)__get_free_pages(GFP_KERNEL, order);
> +               buf[i] = (char *)__get_free_pages(GFP_KERNEL | __GFP_COMP,
> +                                                 order);

Is there a reason __GFP_COMP isn't automatically included in all page
allocations? (Or rather, it seems like the exception is when things
should NOT be considered part of the same allocation, so something
like __GFP_SINGLE should exist?.)

-Kees

>                 if (!buf[i])
>                         goto err_free_buf;
>         }
> --
> 2.21.0.392.gf8f6787159e-goog
>


-- 
Kees Cook