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Message-ID: <CALCETrWE5KzrAC6Os3y0f9CJMnM6znQQSSaexin8CC8JB9q1bQ@mail.gmail.com>
Date: Thu, 9 Mar 2017 09:27:51 -0800
From: Andy Lutomirski <luto@...capital.net>
To: Borislav Petkov <bp@...en8.de>
Cc: Thomas Garnier <thgarnie@...gle.com>, 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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Subject: Re: [PATCH v2 1/4] syscalls: Restore address limit after a syscall
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?
--Andy
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