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From: Jann Horn <jannh@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: "Tobin C. Harding" <tobin@kernel.org>,
	Shuah Khan <shuah@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	kernel list <linux-kernel@vger.kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Daniel Micay <danielmicay@gmail.com>
Subject: Re: [PATCH 5/6] lib: Fix function documentation for strncpy_from_user
Date: Thu, 21 Feb 2019 15:28:13 +0100	[thread overview]
Message-ID: <CAG48ez34MMBfTzQFxj2o5brYDrUS89_gvX9=SnpWZ+TjMUV-BQ@mail.gmail.com> (raw)
In-Reply-To: <CAGXu5jKeS3bkTSXEw2nsjrWoqhbkDZD4C=PdYTHMtM0GNk6tSg@mail.gmail.com>

On Thu, Feb 21, 2019 at 2:05 AM Kees Cook <keescook@chromium.org> wrote:
> On Mon, Feb 18, 2019 at 4:52 PM Jann Horn <jannh@google.com> wrote:
> > AFAICS the byte_at_a_time loop exits when max==0 is reached, and then
> > if `res >= count` (in other words, if we've copied as many bytes as
> > requested, haven't encountered a null byte so far, and haven't reached
> > the end of the address space), we return `res`, which is the same as
> > `count`. Are you sure?
>
> Oh, whew, there is only 1 arch-specific implementation of this. I
> thought you meant there was multiple implementations.

Not sure what you're talking about. Are you talking about
implementations of strncpy_from_user()?


csky: custom strncpy_from_user() calls custom __do_strncpy_from_user,
which is a macro containing a big asm() block.


h8300:
;;; long strncpy_from_user(void *to, void *from, size_t n)
strncpy_from_user:
mov.l er2,er2
bne 1f
sub.l er0,er0
rts
[...]


mips:
static inline long
strncpy_from_user(char *__to, const char __user *__from, long __len)
{
long res;

if (eva_kernel_access()) {
__asm__ __volatile__(
"move\t$4, %1\n\t"
"move\t$5, %2\n\t"
"move\t$6, %3\n\t"
[...]


unicore32:
ENTRY(__strncpy_from_user)
mov ip, r1
1: sub.a r2, r2, #1
ldrusr r3, r1, 1, ns
bfs 2f
stb.w r3, [r0]+, #1
cxor.a r3, #0
[...]


and so on.

> So, generally speaking, I'd love to split all strncpy* uses into
> strscpy_zero() (when expecting to do str->str copies), and some new
> function, named like mempadstr() or str2mem() that copies a str to a
> __nonstring char array, with trailing padding, if there is space. Then
> there is no more mixing the two cases and botching things.

  parent reply	other threads:[~2019-02-21 14:28 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-18 23:23 [PATCH 0/6] lib: Add safe string funtions Tobin C. Harding
2019-02-18 23:23 ` [PATCH 1/6] lib/string: Enable string selftesting Tobin C. Harding
2019-02-19 10:55   ` Andy Shevchenko
2019-02-19 21:55     ` Tobin C. Harding
2019-02-20 10:49       ` Andy Shevchenko
2019-02-20 23:58       ` Kees Cook
2019-02-20 23:57   ` Kees Cook
2019-02-21  5:16     ` Tobin C. Harding
2019-02-18 23:23 ` [PATCH 2/6] lib/string: Fix erroneous 'overflow' documentation Tobin C. Harding
2019-02-21  0:02   ` Kees Cook
2019-02-21  5:17     ` Tobin C. Harding
2019-02-18 23:23 ` [PATCH 3/6] lib/string: Use correct docstring format Tobin C. Harding
2019-02-21  0:07   ` Kees Cook
2019-02-21  4:14     ` Randy Dunlap
2019-02-21  5:27       ` Kees Cook
2019-02-18 23:23 ` [PATCH 4/6] lib/string: Add string copy/zero function Tobin C. Harding
2019-02-21  0:48   ` Kees Cook
2019-02-21  5:20     ` Tobin C. Harding
2019-02-21 12:02     ` Andy Shevchenko
2019-02-25 20:09     ` Tobin C. Harding
2019-02-18 23:23 ` [PATCH 5/6] lib: Fix function documentation for strncpy_from_user Tobin C. Harding
2019-02-19  0:51   ` Jann Horn
2019-02-19 21:52     ` Tobin C. Harding
2019-02-21  1:05     ` Kees Cook
2019-02-21  5:24       ` Tobin C. Harding
2019-02-21  6:02         ` Kees Cook
2019-02-21 14:58           ` Rasmus Villemoes
2019-02-21 23:03             ` Kees Cook
2019-02-25 15:41               ` Rasmus Villemoes
2019-02-21 16:06           ` Jann Horn
2019-02-21 23:14             ` Kees Cook
2019-02-21 20:26           ` Stephen Rothwell
2019-02-21 23:16             ` Kees Cook
2019-02-21 14:28       ` Jann Horn [this message]
2019-02-21 22:52         ` Kees Cook
2019-02-18 23:23 ` [PATCH 6/6] lib: Add function strscpy_from_user() Tobin C. Harding
2019-02-19  2:09   ` Jann Horn
2019-02-19  2:12   ` Jann Horn
2019-02-19 21:53     ` Tobin C. Harding
2019-02-20 23:31 ` [PATCH 0/6] lib: Add safe string funtions Kees Cook
2019-02-21  5:15   ` Tobin C. Harding

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