From: David Laight <David.Laight@ACULAB.COM>
To: 'Arnd Bergmann' <arnd@kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
Christoph Hellwig <hch@infradead.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
Eric Biederman <ebiederm@xmission.com>,
Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
"kexec@lists.infradead.org" <kexec@lists.infradead.org>
Subject: RE: [PATCH v3 1/4] kexec: simplify compat_sys_kexec_load
Date: Tue, 18 May 2021 20:47:36 +0000 [thread overview]
Message-ID: <dcc79c4336234b6a84b597e0e39d65d0@AcuMS.aculab.com> (raw)
In-Reply-To: <20210517203343.3941777-2-arnd@kernel.org>
From: Arnd Bergmann
> Sent: 17 May 2021 21:34
>
> The compat version of sys_kexec_load() uses compat_alloc_user_space to
> convert the user-provided arguments into the native format.
>
> Move the conversion into the regular implementation with
> an in_compat_syscall() check to simplify it and avoid the
> compat_alloc_user_space() call.
>
> compat_sys_kexec_load() now behaves the same as sys_kexec_load().
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> include/linux/kexec.h | 2 -
> kernel/kexec.c | 95 +++++++++++++++++++------------------------
> 2 files changed, 42 insertions(+), 55 deletions(-)
>
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index 0c994ae37729..f61e310d7a85 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -88,14 +88,12 @@ struct kexec_segment {
> size_t memsz;
> };
>
> -#ifdef CONFIG_COMPAT
> struct compat_kexec_segment {
> compat_uptr_t buf;
> compat_size_t bufsz;
> compat_ulong_t mem; /* User space sees this as a (void *) ... */
> compat_size_t memsz;
> };
> -#endif
>
> #ifdef CONFIG_KEXEC_FILE
> struct purgatory_info {
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index c82c6c06f051..6618b1d9f00b 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -19,21 +19,46 @@
>
> #include "kexec_internal.h"
>
> +static int copy_user_compat_segment_list(struct kimage *image,
> + unsigned long nr_segments,
> + void __user *segments)
> +{
> + struct compat_kexec_segment __user *cs = segments;
> + struct compat_kexec_segment segment;
> + int i;
> +
> + for (i = 0; i < nr_segments; i++) {
> + if (copy_from_user(&segment, &cs[i], sizeof(segment)))
> + return -EFAULT;
How many segments are there?
The multiple copy_from_user() will be slow.
> +
> + image->segment[i] = (struct kexec_segment) {
> + .buf = compat_ptr(segment.buf),
> + .bufsz = segment.bufsz,
> + .mem = segment.mem,
> + .memsz = segment.memsz,
> + };
> + }
> +
> + return 0;
> +}
> +
> +
> static int copy_user_segment_list(struct kimage *image,
> unsigned long nr_segments,
> struct kexec_segment __user *segments)
> {
> - int ret;
> size_t segment_bytes;
>
> /* Read in the segments */
> image->nr_segments = nr_segments;
> segment_bytes = nr_segments * sizeof(*segments);
Should there be a bound check on nr_segments?
I can't see one in the code in this patch.
> - ret = copy_from_user(image->segment, segments, segment_bytes);
> - if (ret)
> - ret = -EFAULT;
> + if (in_compat_syscall())
> + return copy_user_compat_segment_list(image, nr_segments, segments);
>
> - return ret;
> + if (copy_from_user(image->segment, segments, segment_bytes))
> + return -EFAULT;
> +
> + return 0;
An alternate sequence (which Eric will like even less!) is to
do a single copy_from_user() for the entire compat size array
into the 'normal' buffer and then do a reverse order conversion
of each array entry from 'compat' to '64 bit'.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-05-18 20:47 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-17 20:33 [PATCH v3 0/4] compat: remove compat_alloc_user_space callers Arnd Bergmann
2021-05-17 20:33 ` [PATCH v3 1/4] kexec: simplify compat_sys_kexec_load Arnd Bergmann
2021-05-18 3:57 ` Eric W. Biederman
2021-05-18 6:40 ` Christoph Hellwig
2021-05-18 7:44 ` Arnd Bergmann
2021-05-18 6:38 ` Christoph Hellwig
2021-05-18 7:47 ` Arnd Bergmann
2021-05-18 13:41 ` Eric W. Biederman
2021-05-18 14:05 ` Arnd Bergmann
2021-05-18 14:17 ` Arnd Bergmann
2021-05-18 16:01 ` Eric W. Biederman
2021-05-18 22:45 ` Eric W. Biederman
2021-05-19 9:55 ` Arnd Bergmann
2021-05-18 20:47 ` David Laight [this message]
2021-05-17 20:33 ` [PATCH v3 2/4] mm: simplify compat_sys_move_pages Arnd Bergmann
2021-05-18 6:42 ` Christoph Hellwig
2021-05-18 20:49 ` David Laight
2021-05-19 13:41 ` Arnd Bergmann
2021-05-17 20:33 ` [PATCH v3 3/4] mm: simplify compat numa syscalls Arnd Bergmann
2021-05-18 6:52 ` Christoph Hellwig
2021-05-17 20:33 ` [PATCH v3 4/4] compat: remove some compat entry points Arnd Bergmann
2021-05-18 6:55 ` Christoph Hellwig
2021-05-19 20:33 ` Thomas Gleixner
2021-05-19 21:00 ` Arnd Bergmann
2021-05-20 9:21 ` Arnd Bergmann
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