[PATCH v2 2/2] kexec: extend kexec_file_load system call

Thiago Jung Bauermann
2016-08-16T00:14:05Z

Here is a new version implementing your suggestions.
I also changed it to kmalloc fdset instead of using the stack.

What do you think?

From: AKASHI Takahiro <takahiro.akashi@linaro.org>

Device tree blob must be passed to a second kernel on DTB-capable
archs, like powerpc and arm64, but the current kernel interface
lacks this support.

This patch extends kexec_file_load system call by adding an extra
argument to this syscall so that an arbitrary number of file descriptors
can be handed out from user space to the kernel.

long sys_kexec_file_load(int kernel_fd, int initrd_fd,
unsigned long cmdline_len,
const char __user *cmdline_ptr,
unsigned long flags,
const struct kexec_fdset __user *ufdset);

If KEXEC_FILE_EXTRA_FDS is set to the "flags" argument, the "ufdset"
argument points to the following struct buffer:

struct kexec_fdset {
int nr_fds;
struct kexec_file_fd fds[0];
}

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
---
include/linux/fs.h | 1 +
include/linux/kexec.h | 7 +++-
include/linux/syscalls.h | 4 +-
include/uapi/linux/kexec.h | 22 +++++++++++
kernel/kexec_file.c | 92 +++++++++++++++++++++++++++++++++++++++++++---
5 files changed, 117 insertions(+), 9 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3523bf62f328..2eb0674392d1 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2656,6 +2656,7 @@ extern int do_pipe_flags(int *, int);
id(MODULE, kernel-module) \
id(KEXEC_IMAGE, kexec-image) \
id(KEXEC_INITRAMFS, kexec-initramfs) \
+ id(KEXEC_PARTIAL_DTB, kexec-partial-dtb)\
id(POLICY, security-policy) \
id(MAX_ID, )

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 4f85d284ed0b..29202935055d 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -148,7 +148,10 @@ struct kexec_file_ops {
kexec_verify_sig_t *verify_sig;
#endif
};
-#endif
+
+int __weak arch_kexec_verify_buffer(enum kexec_file_type type, const void *buf,
+ unsigned long size);
+#endif /* CONFIG_KEXEC_FILE */

struct kimage {
kimage_entry_t head;
@@ -280,7 +283,7 @@ extern int kexec_load_disabled;

/* List of defined/legal kexec file flags */
#define KEXEC_FILE_FLAGS (KEXEC_FILE_UNLOAD | KEXEC_FILE_ON_CRASH | \
- KEXEC_FILE_NO_INITRAMFS)
+ KEXEC_FILE_NO_INITRAMFS | KEXEC_FILE_EXTRA_FDS)

#define VMCOREINFO_BYTES (4096)
#define VMCOREINFO_NOTE_NAME "VMCOREINFO"
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index d02239022bd0..fc072bdb74e3 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -66,6 +66,7 @@ struct perf_event_attr;
struct file_handle;
struct sigaltstack;
union bpf_attr;
+struct kexec_fdset;

#include <linux/types.h>
#include <linux/aio_abi.h>
@@ -321,7 +322,8 @@ asmlinkage long sys_kexec_load(unsigned long entry, unsigned long nr_segments,
asmlinkage long sys_kexec_file_load(int kernel_fd, int initrd_fd,
unsigned long cmdline_len,
const char __user *cmdline_ptr,
- unsigned long flags);
+ unsigned long flags,
+ const struct kexec_fdset __user *ufdset);

asmlinkage long sys_exit(int error_code);
asmlinkage long sys_exit_group(int error_code);
diff --git a/include/uapi/linux/kexec.h b/include/uapi/linux/kexec.h
index aae5ebf2022b..6279be79efba 100644
--- a/include/uapi/linux/kexec.h
+++ b/include/uapi/linux/kexec.h
@@ -23,6 +23,28 @@
#define KEXEC_FILE_UNLOAD 0x00000001
#define KEXEC_FILE_ON_CRASH 0x00000002
#define KEXEC_FILE_NO_INITRAMFS 0x00000004
+#define KEXEC_FILE_EXTRA_FDS 0x00000008
+
+enum kexec_file_type {
+ KEXEC_FILE_TYPE_KERNEL,
+ KEXEC_FILE_TYPE_INITRAMFS,
+
+ /*
+ * Device Tree Blob containing just the nodes and properties that
+ * the kexec_file_load caller wants to add or modify.
+ */
+ KEXEC_FILE_TYPE_PARTIAL_DTB,
+};
+
+struct kexec_file_fd {
+ enum kexec_file_type type;
+ int fd;
+};
+
+struct kexec_fdset {
+ int nr_fds;
+ struct kexec_file_fd fds[0];
+};

/* These values match the ELF architecture values.
* Unless there is a good reason that should continue to be the case.
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 113af2f219b9..302427e5ee71 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -116,6 +116,22 @@ void kimage_file_post_load_cleanup(struct kimage *image)
image->image_loader_data = NULL;
}

+/**
+ * arch_kexec_verify_buffer() - check that the given kexec file is valid
+ *
+ * Device trees in particular can contain properties that may make the kernel
+ * execute code that it wasn't supposed to (e.g., use the wrong entry point
+ * when calling firmware functions). Because of this, the kernel needs to
+ * verify that it is safe to use the device tree blob passed from userspace.
+ *
+ * Return: 0 on success, negative errno on error.
+ */
+int __weak arch_kexec_verify_buffer(enum kexec_file_type type, const void *buf,
+ unsigned long size)
+{
+ return -EINVAL;
+}
+
/*
* In file mode list of segments is prepared by kernel. Copy relevant
* data from user space, do error checking, prepare segment list
@@ -123,11 +139,13 @@ void kimage_file_post_load_cleanup(struct kimage *image)
static int
kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
const char __user *cmdline_ptr,
- unsigned long cmdline_len, unsigned flags)
+ unsigned long cmdline_len, unsigned long flags,
+ const struct kexec_fdset __user *ufdset)
{
int ret = 0;
void *ldata;
loff_t size;
+ struct kexec_fdset *fdset = NULL;

ret = kernel_read_file_from_fd(kernel_fd, &image->kernel_buf,
&size, INT_MAX, READING_KEXEC_IMAGE);
@@ -160,6 +178,64 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
image->initrd_buf_len = size;
}

+ if (flags & KEXEC_FILE_EXTRA_FDS) {
+ int nr_fds, i;
+ size_t fdset_size;
+
+ ret = copy_from_user(&nr_fds, ufdset, sizeof(int));
+ if (ret) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ if (nr_fds < 0 || nr_fds > KEXEC_SEGMENT_MAX) {
+ ret = -E2BIG;
+ goto out;
+ }
+
+ fdset_size = sizeof(struct kexec_fdset)
+ + nr_fds * sizeof(struct kexec_file_fd);
+
+ fdset = kmalloc(fdset_size, GFP_KERNEL);
+ if (fdset == NULL) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ ret = copy_from_user(fdset, ufdset, fdset_size);
+ if (ret) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ if (nr_fds != fdset->nr_fds) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ for (i = 0; i < fdset->nr_fds; i++) {
+ if (fdset->fds[i].type == KEXEC_FILE_TYPE_PARTIAL_DTB) {
+ ret = kernel_read_file_from_fd(fdset->fds[i].fd,
+ &image->dtb_buf, &size, INT_MAX,
+ READING_KEXEC_PARTIAL_DTB);
+ if (ret)
+ goto out;
+ image->dtb_buf_len = size;
+
+ ret = arch_kexec_verify_buffer(KEXEC_FILE_TYPE_PARTIAL_DTB,
+ image->dtb_buf,
+ image->dtb_buf_len);
+ if (ret)
+ goto out;
+ } else {
+ pr_debug("unknown file type %d failed.\n",
+ fdset->fds[i].type);
+ ret = -EINVAL;
+ goto out;
+ }
+ }
+ }
+
if (cmdline_len) {
image->cmdline_buf = kzalloc(cmdline_len, GFP_KERNEL);
if (!image->cmdline_buf) {
@@ -193,6 +269,8 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,

image->image_loader_data = ldata;
out:
+ kfree(fdset);
+
/* In case of error, free up all allocated memory in this function */
if (ret)
kimage_file_post_load_cleanup(image);
@@ -202,7 +280,8 @@ out:
static int
kimage_file_alloc_init(struct kimage **rimage, int kernel_fd,
int initrd_fd, const char __user *cmdline_ptr,
- unsigned long cmdline_len, unsigned long flags)
+ unsigned long cmdline_len, unsigned long flags,
+ const struct kexec_fdset __user *ufdset)
{
int ret;
struct kimage *image;
@@ -221,7 +300,8 @@ kimage_file_alloc_init(struct kimage **rimage, int kernel_fd,
}

ret = kimage_file_prepare_segments(image, kernel_fd, initrd_fd,
- cmdline_ptr, cmdline_len, flags);
+ cmdline_ptr, cmdline_len, flags,
+ ufdset);
if (ret)
goto out_free_image;

@@ -256,9 +336,9 @@ out_free_image:
return ret;
}

-SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
+SYSCALL_DEFINE6(kexec_file_load, int, kernel_fd, int, initrd_fd,
unsigned long, cmdline_len, const char __user *, cmdline_ptr,
- unsigned long, flags)
+ unsigned long, flags, const struct kexec_fdset __user *, ufdset)
{
int ret = 0, i;
struct kimage **dest_image, *image;
@@ -295,7 +375,7 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
kimage_free(xchg(&kexec_crash_image, NULL));

ret = kimage_file_alloc_init(&image, kernel_fd, initrd_fd, cmdline_ptr,
- cmdline_len, flags);
+ cmdline_len, flags, ufdset);
if (ret)
goto out;

--
1.9.1