kexec: Create a temporary file to hold .linux section in uki_probe()

**Problem**
In the arm64 case, a temporary file for kernel is created in
pez_arm64_probe() and passed down to info.kernel_fd later.

However in the x86_64 case, nobody passes a temporary fd to info.kernel_fd,
so finally the fd of the UKI image is passed to syscall. That is not the
expected behavior.

**Situation**
The current framework of kexec-tools passes kernel fd to syscall.
Meanwhile info.kernel_fd presents each probe with an opportunity to
overwhelm the existing kernel fd.

**Solution**
In the UKI probe, a temporary file is created to hold the .linux
section. Later, if no other probe methods set info.kernel_fd, it will be
set in the UKI load method. This way, the correct fd can be passed to
the syscall.

Signed-off-by: Pingfan Liu <[email protected]>
Cc: Simon Horman <[email protected]>
To: [email protected]
Signed-off-by: Simon Horman <[email protected]>

kexec/arch/arm64/kexec-vmlinuz-arm64.c

@@ -104,6 +104,8 @@ int pez_arm64_load(int argc, char **argv, const char *buf, off_t len,
 		off_t nread;
 		int fd;
 
+		if (info->kernel_fd > 0)
+			close(info->kernel_fd);
 		info->kernel_fd = kernel_fd;
 		fd = dup(kernel_fd);
 		if (fd < 0) {

kexec/kexec-uki.c

@@ -15,8 +15,10 @@
 #define UKI_DTB_SECTION ".dtb"
 
 #define FILENAME_UKI_INITRD          "/tmp/InitrdXXXXXX"
+#define FILENAME_UKI_KERNEL          "/tmp/KernelXXXXXX"
 
 static int embeded_linux_format_index = -1;
+static int kernel_fd = -1;
 
 /*
  * Return -1 if not PE, else offset of the PE header
@@ -98,6 +100,15 @@ int uki_image_probe(const char *file_buf, off_t buf_sz)
 	if (linux_sz == -1) {
 		printf("ERR: can not find .linux section\n");
 		return -1;
+	} else {
+		int res;
+
+		res = create_tmpfd(FILENAME_UKI_KERNEL, linux_src, linux_sz,
+					&kernel_fd);
+		if (res < 0) {
+			printf("ERR: can not create tmp file to hold .linux section\n");
+			return -1;
+		}
 	}
 	/*
 	 * After stripping the UKI coat, the real kernel format can be handled now.
@@ -120,6 +131,9 @@ int uki_image_probe(const char *file_buf, off_t buf_sz)
 int uki_image_load(int argc, char **argv, const char *buf, off_t len,
 			struct kexec_info *info)
 {
+	/* In probe() chain, if nobody sets info->kernel_fd, set it now */
+	if (info->kernel_fd == -1)
+		info->kernel_fd = kernel_fd;
 	return file_type[embeded_linux_format_index].load(argc, argv, buf, len, info);
 }