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

Dave Young
2016-08-18T08:20:09Z

Since Eric was objecting the extension, I think you should convince him,
but I will review from code point of view.

On 08/11/16 at 08:03pm, Thiago Jung Bauermann wrote:
> 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 | 83 ++++++++++++++++++++++++++++++++++++++++++----
> 5 files changed, 108 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3523bf62f328..847d9c31f428 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..d6803dd884e2 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -25,6 +25,9 @@
> #include <linux/vmalloc.h>
> #include "kexec_internal.h"
>
> +#define MAX_FDSET_SIZE (sizeof(struct kexec_fdset) + \
> + KEXEC_SEGMENT_MAX * sizeof(struct kexec_file_fd))

How about use KEXEC_EXTRA_FD_MAX = 1, so only allow passing one fd for
now. In the future if there's other requirement we can extend the
internal value.

> +
> /*
> * Declare these symbols weak so that if architecture provides a purgatory,
> * these will be overridden.
> @@ -116,6 +119,22 @@ 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
> @@ -123,7 +142,8 @@ 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;
> @@ -160,6 +180,55 @@ 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;
> + char fdset_buf[MAX_FDSET_SIZE];
> + struct kexec_fdset *fdset = (struct kexec_fdset *) fdset_buf;
> +
> + ret = copy_from_user(&nr_fds, ufdset, sizeof(int));
> + if (ret) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + if (nr_fds > KEXEC_SEGMENT_MAX) {
> + ret = -E2BIG;
> + goto out;
> + }
> +
> + fdset_size = sizeof(struct kexec_fdset)
> + + nr_fds * sizeof(struct kexec_file_fd);
> +
> + ret = copy_from_user(fdset, ufdset, fdset_size);
> + if (ret) {
> + 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);

Should be pr_err

> + ret = -EINVAL;
> + goto out;
> + }
> + }
> + }
> +
> if (cmdline_len) {
> image->cmdline_buf = kzalloc(cmdline_len, GFP_KERNEL);
> if (!image->cmdline_buf) {
> @@ -202,7 +271,8 @@ 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 +291,8 @@ 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 +327,9 @@ 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 +366,7 @@ 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
>
>
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> kexec mailing list
> kexec@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec

Thanks
Dave