From: Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Thomas Garnier <thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: "Martin Schwidefsky"
<schwidefsky-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>,
"Heiko Carstens"
<heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>,
"Dave Hansen"
<dave.hansen-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
"Arnd Bergmann" <arnd-r2nGTMty4D4@public.gmane.org>,
"David Howells"
<dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"René Nyffenegger"
<mail-gLCNRsNSrVdVZEhyV+6z5nIPMjoJpjVV@public.gmane.org>,
"Andrew Morton"
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
"Paul E . McKenney"
<paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>,
"Eric W . Biederman"
<ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>,
"Thomas Gleixner" <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
"Oleg Nesterov" <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"Pavel Tikhomirov"
<ptikhomirov-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>,
"Ingo Molnar" <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"H . Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>,
"Andy Lutomirski" <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
"Paolo Bonzini"
<pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"Kees Cook" <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
"Rik van Riel" <riel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"Josh Poimboeuf" <jpoimboe@redhat.c>
Subject: Re: [PATCH v8 1/4] syscalls: Verify address limit before returning to user-mode
Date: Thu, 27 Apr 2017 08:49:17 +0200 [thread overview]
Message-ID: <20170427064917.phwo6yl4v4q43fql@gmail.com> (raw)
In-Reply-To: <20170426183425.32158-1-thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
* Thomas Garnier <thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> wrote:
> +
> +/*
> + * Called before coming back to user-mode. Returning to user-mode with an
> + * address limit different than USER_DS can allow to overwrite kernel memory.
> + */
> +static inline void addr_limit_check_syscall(void)
> +{
> + BUG_ON(!segment_eq(get_fs(), USER_DS));
> +}
> +
> +#ifndef CONFIG_ADDR_LIMIT_CHECK
> +#define __CHECK_USERMODE_SYSCALL() \
> + bool user_caller = segment_eq(get_fs(), USER_DS)
> +#define __VERIFY_ADDR_LIMIT() \
> + if (user_caller) addr_limit_check_syscall()
> +#else
> +#define __CHECK_USERMODE_SYSCALL()
> +#define __VERIFY_ADDR_LIMIT()
> +asmlinkage void addr_limit_check_failed(void) __noreturn;
> +#endif
_Please_ harmonize all the externally exposed names and symbols.
There's no reason for this mismash of names:
CONFIG_ADDR_LIMIT_CHECK
__CHECK_USERMODE_SYSCALL
__VERIFY_ADDR_LIMIT
When we could just as easily name them consistently, along the existing pattern:
CONFIG_ADDR_LIMIT_CHECK
__SYSCALL_ADDR_LIMIT_CHECK
__ADDR_LIMIT_CHECK
which should fit into existing nomenclature:
> #define __SYSCALL_DEFINEx(x, name, ...) \
But even with that fixed, the whole construct still looks pretty weird:
> { \
> - long ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \
> + long ret; \
> + __CHECK_USERMODE_SYSCALL(); \
> + ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \
> + __ADDR_LIMIT_CHECK(); \
> __MAP(x,__SC_TEST,__VA_ARGS__); \
> __PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \
> return ret; \
I think something like this would be more natural to read:
> + ADDR_LIMIT_CHECK_PRE(); \
> + ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \
> + ADDR_LIMIT_CHECK_POST(); \
it's a clear pre/post construct. Also note the lack of double underscores.
BTW., a further simplification would be:
#ifndef ADDR_LIMIT_CHECK_PRE
# define ADDR_LIMIT_CHECK_PRE ...
#endif
This way architectures could override this generic functionality simply by
defining the helpers. Architectures that don't do that get the generic version.
Thanks,
Ingo
next prev parent reply other threads:[~2017-04-27 6:49 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-26 18:34 [PATCH v8 1/4] syscalls: Verify address limit before returning to user-mode Thomas Garnier
2017-04-26 18:34 ` [PATCH v8 2/4] x86/syscalls: Optimize address limit check Thomas Garnier
2017-04-26 18:34 ` [PATCH v8 3/4] arm/syscalls: " Thomas Garnier
2017-04-26 18:34 ` [PATCH v8 4/4] arm64/syscalls: " Thomas Garnier
[not found] ` <20170426183425.32158-1-thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2017-04-27 6:49 ` Ingo Molnar [this message]
2017-04-27 14:16 ` [PATCH v8 1/4] syscalls: Verify address limit before returning to user-mode Thomas Garnier
[not found] ` <CAJcbSZENjCgn3TNDGzCBBSOXMvbTX8mBO7Trugdb5VRzhxwmHg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-04-27 14:42 ` Thomas Garnier
[not found] ` <20170427144227.113630-1-thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2017-04-28 6:35 ` Ingo Molnar
2017-04-28 6:33 ` Ingo Molnar
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