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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>

  parent reply	other threads:[~2020-05-16  3:43 UTC|newest]

Thread overview: 54+ 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 19:11     ` 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 23:03           ` Linus Torvalds
2020-05-13 23:24           ` Daniel Borkmann
2020-05-13 23:20         ` Masami Hiramatsu
2020-05-13 23:59           ` Linus Torvalds
2020-05-13 23:59             ` Linus Torvalds
2020-05-14  1:00             ` Masami Hiramatsu
2020-05-14  2:43               ` Linus Torvalds
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 19:36     ` Linus Torvalds
2020-05-13 19:40     ` Christoph Hellwig
2020-05-13 19:48       ` Linus Torvalds
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 19:37   ` Linus Torvalds
2020-05-13 23:04 ` Daniel Borkmann
2020-05-13 23:20   ` Linus Torvalds
2020-05-13 23:20     ` Linus Torvalds
2020-05-19  5:50   ` Christoph Hellwig

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