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ANDROID: cfi: ensure RCU is watching in __cfi_slowpath

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Indirect calls can happen when RCU is not watching, so we need to wake
it up again for the CFI shadow and __module_address. As these calls can
happen anywhere, use rcu_nmi_enter() similarly to kernel_text_address(),
and switch to rcu_read_lock_sched() for shadow access.

Bug: 169017431
Change-Id: Iebb857df898e644b4952a62d86fa5ff9852b5711
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
This commit is contained in:
Sami Tolvanen 2020-10-16 09:19:23 -07:00 committed by Alistair Delva
parent 77bc008d89
commit d0dc5d8586
1 changed files with 22 additions and 12 deletions
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34
kernel/cfi.c
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@ -6,6 +6,7 @@
*/
#include <linux/gfp.h>
#include <linux/hardirq.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/printk.h>
@ -246,33 +247,36 @@ static inline cfi_check_fn ptr_to_check_fn(const struct cfi_shadow __rcu *s,
static inline cfi_check_fn find_module_cfi_check(void *ptr)
{
cfi_check_fn f = CFI_CHECK_FN;
struct module *mod;
preempt_disable();
mod = __module_address((unsigned long)ptr);
if (mod)
f = mod->cfi_check;
preempt_enable();
if (mod)
return mod->cfi_check;
return CFI_CHECK_FN;
return f;
}
static inline cfi_check_fn find_cfi_check(void *ptr)
{
#ifdef CONFIG_CFI_CLANG_SHADOW
bool rcu;
cfi_check_fn f;
if (!rcu_access_pointer(cfi_shadow))
return CFI_CHECK_FN; /* No loaded modules */
rcu = rcu_is_watching();
if (!rcu)
rcu_nmi_enter();
#ifdef CONFIG_CFI_CLANG_SHADOW
/* Look up the __cfi_check function to use */
rcu_read_lock();
f = ptr_to_check_fn(rcu_dereference(cfi_shadow), (unsigned long)ptr);
rcu_read_unlock();
rcu_read_lock_sched();
f = ptr_to_check_fn(rcu_dereference_sched(cfi_shadow),
(unsigned long)ptr);
rcu_read_unlock_sched();
if (f)
return f;
goto out;
/*
* Fall back to find_module_cfi_check, which works also for a larger
@ -280,7 +284,13 @@ static inline cfi_check_fn find_cfi_check(void *ptr)
*/
#endif /* CONFIG_CFI_CLANG_SHADOW */
return find_module_cfi_check(ptr);
f = find_module_cfi_check(ptr);
out:
if (!rcu)
rcu_nmi_exit();
return f;
}
void cfi_slowpath_handler(uint64_t id, void *ptr, void *diag)