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Subject[PATCH 24/45] kexec: call do_kexec_load() in compat syscall directly
Date
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 tries to remove in-kernel calls to
syscalls. On this basis, the syscall entry path can be streamlined.

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: kexec@lists.infradead.org
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
---
kernel/kexec.c | 50 +++++++++++++++++++++++++++++++++++++-------------
1 file changed, 37 insertions(+), 13 deletions(-)

diff --git a/kernel/kexec.c b/kernel/kexec.c
index e62ec4dc6620..d959dc2c5587 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -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 +283,19 @@ 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);
}
#endif
--
2.16.2
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