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

Sent: 17 May 2021 21:34

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 <arnd@arndb.de>
---
 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;