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Message-ID: <CAJcbSZG1WR5QktwEsfe0MCyRW+1gKJg3axM29QkF-=J4qe6uYg@mail.gmail.com>
Date: Thu, 9 Mar 2017 09:41:14 -0800
From: Thomas Garnier <thgarnie@...gle.com>
To: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>, David Howells <dhowells@...hat.com>,
Dave Hansen <dave.hansen@...el.com>, Arnd Bergmann <arnd@...db.de>, Al Viro <viro@...iv.linux.org.uk>,
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Andrew Morton <akpm@...ux-foundation.org>, Kees Cook <keescook@...omium.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, "David S . Miller" <davem@...emloft.net>,
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Subject: Re: [PATCH v2 1/4] syscalls: Restore address limit after a syscall
On Thu, Mar 9, 2017 at 9:27 AM, Andy Lutomirski <luto@...capital.net> wrote:
> On Thu, Mar 9, 2017 at 12:42 AM, Borislav Petkov <bp@...en8.de> wrote:
>> On Wed, Mar 08, 2017 at 05:24:53PM -0800, Thomas Garnier wrote:
>>> @@ -191,6 +191,22 @@ extern struct trace_event_functions exit_syscall_print_funcs;
>>> SYSCALL_METADATA(sname, x, __VA_ARGS__) \
>>> __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
>>>
>>> +asmlinkage void verify_pre_usermode_state(void);
>>> +
>>> +#ifndef CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
>>> +static inline bool has_user_ds(void) {
>>> + bool ret = segment_eq(get_fs(), USER_DS);
>>> + // Prevent re-ordering the call
>>
>> This is not the kernel comments style. Use /* */ instead.
>>
>>> + barrier();
>>> + return ret;
>>> +}
>>> +#else
>>> +static inline bool has_user_ds(void) {
>>> + return false;
>>> +}
>>> +#endif
>>
>> ... and then you could slim down the ifdeffery a bit:
>>
>> static inline bool has_user_ds(void) {
>> bool ret = false;
>>
>> #ifndef CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
>> ret = segment_eq(get_fs(), USER_DS);
>> /* Prevent re-ordering the call. */
>> barrier();
>> #endif
>>
>> return ret;
>> }
>
> I don't like having any kernel configuration in which has_user_ds()
> unconditionally returns false. Can we put the ifdeffery in the caller
> instead?
I don't like it either to be honest. We could have something like:
#ifndef CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
#define CHECK_USER_CALLER(_x) bool _x = segment_eq(get_fs(), USER_DS)
#else
#define CHECK_USER_CALLER(_x) bool _x = false
#endif
// In the syscall macro:
CHECK_CALLED_BY_USER(user_caller);
>
> --Andy
--
Thomas
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