Subject: [PATCH v3 1/4] kexec: simplify compat_sys_kexec_load

From: Arnd Bergmann <[email-masked]>
Date: Mon, 17 May 2021 22:33:40 +0200

From: Arnd Bergmann <[email-masked]>

The compat version of sys_kexec_load() uses compat_alloc_user_space to
convert the user-provided arguments into the native format.

Move the conversion into the regular implementation with
an in_compat_syscall() check to simplify it and avoid the
compat_alloc_user_space() call.

compat_sys_kexec_load() now behaves the same as sys_kexec_load().

Signed-off-by: Arnd Bergmann <[email-masked]>
---
 include/linux/kexec.h |  2 -
 kernel/kexec.c        | 95 +++++++++++++++++++------------------------
 2 files changed, 42 insertions(+), 55 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 0c994ae37729..f61e310d7a85 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -88,14 +88,12 @@ struct kexec_segment {
 	size_t memsz;
 };
 
-#ifdef CONFIG_COMPAT
 struct compat_kexec_segment {
 	compat_uptr_t buf;
 	compat_size_t bufsz;
 	compat_ulong_t mem;	/* User space sees this as a (void *) ... */
 	compat_size_t memsz;
 };
-#endif
 
 #ifdef CONFIG_KEXEC_FILE
 struct purgatory_info {
diff --git a/kernel/kexec.c b/kernel/kexec.c
index c82c6c06f051..6618b1d9f00b 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -19,21 +19,46 @@
 
 #include "kexec_internal.h"
 
+static int copy_user_compat_segment_list(struct kimage *image,
+					 unsigned long nr_segments,
+					 void __user *segments)
+{
+	struct compat_kexec_segment __user *cs = segments;
+	struct compat_kexec_segment segment;
+	int i;
+
+	for (i = 0; i < nr_segments; i++) {
+		if (copy_from_user(&segment, &cs[i], sizeof(segment)))
+			return -EFAULT;
+
+		image->segment[i] = (struct kexec_segment) {
+			.buf   = compat_ptr(segment.buf),
+			.bufsz = segment.bufsz,
+			.mem   = segment.mem,
+			.memsz = segment.memsz,
+		};
+	}
+
+	return 0;
+}
+
+
 static int copy_user_segment_list(struct kimage *image,
 				  unsigned long nr_segments,
 				  struct kexec_segment __user *segments)
 {
-	int ret;
 	size_t segment_bytes;
 
 	/* Read in the segments */
 	image->nr_segments = nr_segments;
 	segment_bytes = nr_segments * sizeof(*segments);
-	ret = copy_from_user(image->segment, segments, segment_bytes);
-	if (ret)
-		ret = -EFAULT;
+	if (in_compat_syscall())
+		return copy_user_compat_segment_list(image, nr_segments, segments);
 
-	return ret;
+	if (copy_from_user(image->segment, segments, segment_bytes))
+		return -EFAULT;
+
+	return 0;
 }
 
 static int kimage_alloc_init(struct kimage **rimage, unsigned long entry,
@@ -233,8 +258,9 @@ static inline int kexec_load_check(unsigned long nr_segments,
 	return 0;
 }
 
-SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
-		struct kexec_segment __user *, segments, unsigned long, flags)
+static int kernel_kexec_load(unsigned long entry, unsigned long nr_segments,
+			     struct kexec_segment __user * segments,
+			     unsigned long flags)
 {
 	int result;
 
@@ -265,57 +291,20 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
 	return result;
 }
 
+SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
+		struct kexec_segment __user *, segments, unsigned long, flags)
+{
+	return kernel_kexec_load(entry, nr_segments, segments, flags);
+}
+
 #ifdef CONFIG_COMPAT
 COMPAT_SYSCALL_DEFINE4(kexec_load, compat_ulong_t, entry,
 		       compat_ulong_t, nr_segments,
 		       struct compat_kexec_segment __user *, segments,
 		       compat_ulong_t, flags)
 {
-	struct compat_kexec_segment in;
-	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;
-
-	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));
-		if (result)
-			return -EFAULT;
-
-		out.buf   = compat_ptr(in.buf);
-		out.bufsz = in.bufsz;
-		out.mem   = in.mem;
-		out.memsz = in.memsz;
-
-		result = copy_to_user(&ksegments[i], &out, sizeof(out));
-		if (result)
-			return -EFAULT;
-	}
-
-	/* 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;
+	return kernel_kexec_load(entry, nr_segments,
+				 (struct kexec_segment __user *)segments,
+				 flags);
 }
 #endif
-- 
2.29.2

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