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Commit 6b27aef0 authored by Dominik Brodowski's avatar Dominik Brodowski
Browse files

kexec: call do_kexec_load() in compat syscall directly 

do_kexec_load() can be called directly by compat_sys_kexec() as long as
the same parameters checks are completed which are currently handled
(also) by sys_kexec(). Therefore, move those to kexec_load_check(),
call that newly introduced helper function from both sys_kexec() and
compat_sys_kexec(), and duplicate the remaining code from sys_kexec()
in compat_sys_kexec().

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net



Cc: Eric Biederman <ebiederm@xmission.com>
Cc: kexec@lists.infradead.org
Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
parent d53238cd

kernel/kexec.c

+39 −13
Original line number Diff line number Diff line
@@ -192,11 +192,9 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments, 
 * that to happen you need to do that yourself.

 */



SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,

		struct kexec_segment __user *, segments, unsigned long, flags)

static inline int kexec_load_check(unsigned long nr_segments,

				   unsigned long flags)

{

	int result;



	/* We only trust the superuser with rebooting the system. */

	if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)

		return -EPERM;
@@ -208,17 +206,29 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments, 
	if ((flags & KEXEC_FLAGS) != (flags & ~KEXEC_ARCH_MASK))

		return -EINVAL;



	/* Verify we are on the appropriate architecture */

	if (((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH) &&

		((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))

		return -EINVAL;



	/* Put an artificial cap on the number

	 * of segments passed to kexec_load.

	 */

	if (nr_segments > KEXEC_SEGMENT_MAX)

		return -EINVAL;



	return 0;

}



SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,

		struct kexec_segment __user *, segments, unsigned long, flags)

{

	int result;



	result = kexec_load_check(nr_segments, flags);

	if (result)

		return result;



	/* Verify we are on the appropriate architecture */

	if (((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH) &&

		((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))

		return -EINVAL;



	/* Because we write directly to the reserved memory

	 * region when loading crash kernels we need a mutex here to

	 * prevent multiple crash  kernels from attempting to load
@@ -247,15 +257,16 @@ COMPAT_SYSCALL_DEFINE4(kexec_load, compat_ulong_t, entry, 
	struct kexec_segment out, __user *ksegments;

	unsigned long i, result;



	result = kexec_load_check(nr_segments, flags);

	if (result)

		return result;



	/* Don't allow clients that don't understand the native

	 * architecture to do anything.

	 */

	if ((flags & KEXEC_ARCH_MASK) == KEXEC_ARCH_DEFAULT)

		return -EINVAL;



	if (nr_segments > KEXEC_SEGMENT_MAX)

		return -EINVAL;



	ksegments = compat_alloc_user_space(nr_segments * sizeof(out));

	for (i = 0; i < nr_segments; i++) {

		result = copy_from_user(&in, &segments[i], sizeof(in));
@@ -272,6 +283,21 @@ COMPAT_SYSCALL_DEFINE4(kexec_load, compat_ulong_t, entry, 
			return -EFAULT;

	}



	return sys_kexec_load(entry, nr_segments, ksegments, flags);

	/* Because we write directly to the reserved memory

	 * region when loading crash kernels we need a mutex here to

	 * prevent multiple crash  kernels from attempting to load

	 * simultaneously, and to prevent a crash kernel from loading

	 * over the top of a in use crash kernel.

	 *

	 * KISS: always take the mutex.

	 */

	if (!mutex_trylock(&kexec_mutex))

		return -EBUSY;



	result = do_kexec_load(entry, nr_segments, ksegments, flags);



	mutex_unlock(&kexec_mutex);



	return result;

}

#endif