From: Masami Hiramatsu <mhiramat@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: x86@kernel.org, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-parisc@vger.kernel.org, linux-um@lists.infradead.org,
netdev@vger.kernel.org, bpf@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 14/18] maccess: allow architectures to provide kernel probing directly
Date: Sat, 16 May 2020 12:42:59 +0900 [thread overview]
Message-ID: <20200516124259.5b68a4e1d4670efa1397a1e0@kernel.org> (raw)
In-Reply-To: <20200513160038.2482415-15-hch@lst.de>
Hi Christoph,
On Wed, 13 May 2020 18:00:34 +0200
Christoph Hellwig <hch@lst.de> wrote:
> Provide alternative versions of probe_kernel_read, probe_kernel_write
> and strncpy_from_kernel_unsafe that don't need set_fs magic, but instead
> use arch hooks that are modelled after unsafe_{get,put}_user to access
> kernel memory in an exception safe way.
This patch seems to introduce new implementation of probe_kernel_read/write()
and strncpy_from_kernel_unsafe(), but also drops copy_from/to_kernel_nofault()
and strncpy_from_kernel_nofault() if HAVE_ARCH_PROBE_KERNEL is defined.
In the result, this cause a link error with BPF and kprobe events.
BTW, what is the difference of *_unsafe() and *_nofault()?
(maybe we make those to *_nofault() finally?)
Thank you,
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> mm/maccess.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 76 insertions(+)
>
> diff --git a/mm/maccess.c b/mm/maccess.c
> index 9773e2253b495..e9efe2f98e34a 100644
> --- a/mm/maccess.c
> +++ b/mm/maccess.c
> @@ -12,6 +12,81 @@ bool __weak probe_kernel_read_allowed(void *dst, const void *unsafe_src,
> return true;
> }
>
> +#ifdef HAVE_ARCH_PROBE_KERNEL
> +
> +#define probe_kernel_read_loop(dst, src, len, type, err_label) \
> + while (len >= sizeof(type)) { \
> + arch_kernel_read(dst, src, type, err_label); \
> + dst += sizeof(type); \
> + src += sizeof(type); \
> + len -= sizeof(type); \
> + }
> +
> +long probe_kernel_read(void *dst, const void *src, size_t size)
> +{
> + if (!probe_kernel_read_allowed(dst, src, size))
> + return -EFAULT;
> +
> + pagefault_disable();
> + probe_kernel_read_loop(dst, src, size, u64, Efault);
> + probe_kernel_read_loop(dst, src, size, u32, Efault);
> + probe_kernel_read_loop(dst, src, size, u16, Efault);
> + probe_kernel_read_loop(dst, src, size, u8, Efault);
> + pagefault_enable();
> + return 0;
> +Efault:
> + pagefault_enable();
> + return -EFAULT;
> +}
> +EXPORT_SYMBOL_GPL(probe_kernel_read);
> +
> +#define probe_kernel_write_loop(dst, src, len, type, err_label) \
> + while (len >= sizeof(type)) { \
> + arch_kernel_write(dst, src, type, err_label); \
> + dst += sizeof(type); \
> + src += sizeof(type); \
> + len -= sizeof(type); \
> + }
> +
> +long probe_kernel_write(void *dst, const void *src, size_t size)
> +{
> + pagefault_disable();
> + probe_kernel_write_loop(dst, src, size, u64, Efault);
> + probe_kernel_write_loop(dst, src, size, u32, Efault);
> + probe_kernel_write_loop(dst, src, size, u16, Efault);
> + probe_kernel_write_loop(dst, src, size, u8, Efault);
> + pagefault_enable();
> + return 0;
> +Efault:
> + pagefault_enable();
> + return -EFAULT;
> +}
> +
> +long strncpy_from_kernel_unsafe(char *dst, const void *unsafe_addr, long count)
> +{
> + const void *src = unsafe_addr;
> +
> + if (unlikely(count <= 0))
> + return 0;
> + if (!probe_kernel_read_allowed(dst, unsafe_addr, count))
> + return -EFAULT;
> +
> + pagefault_disable();
> + do {
> + arch_kernel_read(dst, src, u8, Efault);
> + dst++;
> + src++;
> + } while (dst[-1] && src - unsafe_addr < count);
> + pagefault_enable();
> +
> + dst[-1] = '\0';
> + return src - unsafe_addr;
> +Efault:
> + pagefault_enable();
> + dst[-1] = '\0';
> + return -EFAULT;
> +}
> +#else /* HAVE_ARCH_PROBE_KERNEL */
> /**
> * probe_kernel_read(): safely attempt to read from kernel-space
> * @dst: pointer to the buffer that shall take the data
> @@ -114,6 +189,7 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
>
> return ret ? -EFAULT : src - unsafe_addr;
> }
> +#endif /* HAVE_ARCH_PROBE_KERNEL */
>
> /**
> * probe_user_read(): safely attempt to read from a user-space location
> --
> 2.26.2
>
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2020-05-16 3:43 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-13 16:00 clean up and streamline probe_kernel_* and friends v2 Christoph Hellwig
2020-05-13 16:00 ` [PATCH 01/18] maccess: unexport probe_kernel_write and probe_user_write Christoph Hellwig
2020-05-13 16:00 ` [PATCH 02/18] maccess: remove various unused weak aliases Christoph Hellwig
2020-05-13 16:00 ` [PATCH 03/18] maccess: remove duplicate kerneldoc comments Christoph Hellwig
2020-05-13 16:00 ` [PATCH 04/18] maccess: clarify " Christoph Hellwig
2020-05-13 16:00 ` [PATCH 05/18] maccess: update the top of file comment Christoph Hellwig
2020-05-13 16:00 ` [PATCH 06/18] maccess: rename strncpy_from_unsafe_user to strncpy_from_user_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 07/18] maccess: rename strncpy_from_unsafe_strict to strncpy_from_kernel_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 08/18] maccess: rename strnlen_unsafe_user to strnlen_user_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 09/18] maccess: remove probe_read_common and probe_write_common Christoph Hellwig
2020-05-13 16:00 ` [PATCH 10/18] maccess: unify the probe kernel arch hooks Christoph Hellwig
2020-05-14 1:13 ` Masami Hiramatsu
2020-05-19 5:46 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 11/18] maccess: remove strncpy_from_unsafe Christoph Hellwig
2020-05-13 19:11 ` Linus Torvalds
2020-05-13 19:28 ` Christoph Hellwig
2020-05-13 22:36 ` Daniel Borkmann
2020-05-13 23:03 ` Linus Torvalds
2020-05-13 23:24 ` Daniel Borkmann
2020-05-13 23:20 ` Masami Hiramatsu
2020-05-13 23:59 ` Linus Torvalds
2020-05-14 1:00 ` Masami Hiramatsu
2020-05-14 2:43 ` Linus Torvalds
2020-05-14 9:44 ` Masami Hiramatsu
2020-05-14 10:27 ` Daniel Borkmann
2020-05-13 23:28 ` Al Viro
2020-05-13 23:58 ` Daniel Borkmann
2020-05-14 10:01 ` David Laight
2020-05-14 10:21 ` Daniel Borkmann
2020-05-13 16:00 ` [PATCH 12/18] maccess: always use strict semantics for probe_kernel_read Christoph Hellwig
2020-05-13 16:00 ` [PATCH 13/18] maccess: move user access routines together Christoph Hellwig
2020-05-13 16:00 ` [PATCH 14/18] maccess: allow architectures to provide kernel probing directly Christoph Hellwig
2020-05-13 19:36 ` Linus Torvalds
2020-05-13 19:40 ` Christoph Hellwig
2020-05-13 19:48 ` Linus Torvalds
2020-05-13 19:54 ` Christoph Hellwig
2020-05-16 3:42 ` Masami Hiramatsu [this message]
2020-05-18 15:09 ` Christoph Hellwig
2020-05-13 16:00 ` [PATCH 15/18] x86: use non-set_fs based maccess routines Christoph Hellwig
2020-05-13 16:00 ` [PATCH 16/18] maccess: rename probe_kernel_{read,write} to copy_{from,to}_kernel_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 17/18] maccess: rename probe_user_{read,write} to copy_{from,to}_user_nofault Christoph Hellwig
2020-05-13 16:00 ` [PATCH 18/18] maccess: rename probe_kernel_address to get_kernel_nofault Christoph Hellwig
2020-05-13 19:37 ` clean up and streamline probe_kernel_* and friends v2 Linus Torvalds
2020-05-13 23:04 ` Daniel Borkmann
2020-05-13 23:20 ` Linus Torvalds
2020-05-19 5:50 ` Christoph Hellwig
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200516124259.5b68a4e1d4670efa1397a1e0@kernel.org \
--to=mhiramat@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=hch@lst.de \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-parisc@vger.kernel.org \
--cc=linux-um@lists.infradead.org \
--cc=netdev@vger.kernel.org \
--cc=torvalds@linux-foundation.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).