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    SubjectRe: [PATCH 3/3 V13] RO/NX protection for loadable kernel
    Hi,

    Le Mon, 29 Nov 2010 13:15:42 -0500,
    Steven Rostedt <rostedt@goodmis.org> a écrit :

    > This patch breaks function tracer:
    >
    > ------------[ cut here ]------------
    > WARNING: at kernel/trace/ftrace.c:1014 ftrace_bug+0x114/0x171()
    > Hardware name: Precision WorkStation 470
    > Modules linked in: i2c_core(+)
    > Pid: 86, comm: modprobe Not tainted 2.6.37-rc2+ #68
    > Call Trace:
    > [<ffffffff8104e957>] warn_slowpath_common+0x85/0x9d
    > [<ffffffffa00026db>] ? __process_new_adapter+0x7/0x34 [i2c_core]
    > [<ffffffffa00026db>] ? __process_new_adapter+0x7/0x34 [i2c_core]
    > [<ffffffff8104e989>] warn_slowpath_null+0x1a/0x1c
    > [<ffffffff810a9dfe>] ftrace_bug+0x114/0x171
    > [<ffffffffa00026db>] ? __process_new_adapter+0x7/0x34 [i2c_core]
    > [<ffffffff810aa0db>] ftrace_process_locs+0x1ae/0x274
    > [<ffffffffa00026db>] ? __process_new_adapter+0x7/0x34 [i2c_core]
    > [<ffffffff810aa29e>] ftrace_module_notify+0x39/0x44
    > [<ffffffff814405cf>] notifier_call_chain+0x37/0x63
    > [<ffffffff8106e054>] __blocking_notifier_call_chain+0x46/0x5b
    > [<ffffffff8106e07d>] blocking_notifier_call_chain+0x14/0x16
    > [<ffffffff8107ffde>] sys_init_module+0x73/0x1f3
    > [<ffffffff8100acf2>] system_call_fastpath+0x16/0x1b
    > ---[ end trace 2aff4f4ca53ec746 ]---
    > ftrace faulted on writing [<ffffffffa00026db>]
    > __process_new_adapter+0x7/0x34 [i2c_core]
    >
    >
    > On Tue, Nov 16, 2010 at 10:35:16PM +0100, matthieu castet wrote:
    > >
    > > @@ -2650,6 +2810,18 @@ static struct module *load_module(void
    > > __user *umod, kfree(info.strmap);
    > > free_copy(&info);
    > >
    > > + /* Set RO and NX regions for core */
    > > + set_section_ro_nx(mod->module_core,
    > > + mod->core_text_size,
    > > + mod->core_ro_size,
    > > + mod->core_size);
    > > +
    > > + /* Set RO and NX regions for init */
    > > + set_section_ro_nx(mod->module_init,
    > > + mod->init_text_size,
    > > + mod->init_ro_size,
    > > + mod->init_size);
    > > +
    >
    > Here we set the text read only before we call the notifiers. The
    > function tracer changes the calls to mcount into nops via a notifier
    > call so this must be done after the module notifiers.
    >
    > > /* Done! */
    > > trace_module_load(mod);
    > > return mod;
    > > @@ -2753,6 +2925,7 @@ SYSCALL_DEFINE3(init_module, void __user *,
    > > umod, mod->symtab = mod->core_symtab;
    > > mod->strtab = mod->core_strtab;
    > > #endif
    > > + unset_section_ro_nx(mod, mod->module_init);
    > > module_free(mod, mod->module_init);
    > > mod->module_init = NULL;
    > > mod->init_size = 0;
    >
    > Below is the patch that fixes this bug.
    >
    > -- Steve
    >
    > Reported-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    >
    > diff --git a/kernel/module.c b/kernel/module.c
    > index ba421e6..5ccf52c 100644
    > --- a/kernel/module.c
    > +++ b/kernel/module.c
    > @@ -2804,18 +2804,6 @@ static struct module *load_module(void __user
    > *umod, kfree(info.strmap);
    > free_copy(&info);
    >
    > - /* Set RO and NX regions for core */
    > - set_section_ro_nx(mod->module_core,
    > - mod->core_text_size,
    > - mod->core_ro_size,
    > - mod->core_size);
    > -
    > - /* Set RO and NX regions for init */
    > - set_section_ro_nx(mod->module_init,
    > - mod->init_text_size,
    > - mod->init_ro_size,
    > - mod->init_size);
    > -
    > /* Done! */
    > trace_module_load(mod);
    > return mod;
    > @@ -2876,6 +2864,18 @@ SYSCALL_DEFINE3(init_module, void __user *,
    > umod, blocking_notifier_call_chain(&module_notify_list,
    > MODULE_STATE_COMING, mod);
    >
    > + /* Set RO and NX regions for core */
    > + set_section_ro_nx(mod->module_core,
    > + mod->core_text_size,
    > + mod->core_ro_size,
    > + mod->core_size);
    > +
    > + /* Set RO and NX regions for init */
    > + set_section_ro_nx(mod->module_init,
    > + mod->init_text_size,
    > + mod->init_ro_size,
    > + mod->init_size);
    > +
    > do_mod_ctors(mod);
    > /* Start the module */
    > if (mod->init != NULL)
    >
    >

    That's look fine for me.

    But I wonder why ftrace_arch_code_modify_prepare isn't called ?

    It is only called when we start/stop tracing ?

    Matthieu
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