On 20/10/2020 13:30, Andre Przywara wrote:
Hi,
> Commit c9acdae1d2e7 ("arm64: Use default kernel offset when the image
> file can't be seeked") "guessed" the arm64 kernel offset to be the old
> default of 512K if the file descriptor for the kernel image could not
> be seeked. This mostly works today because most modern kernels are
> somewhat forgiving when loaded at the wrong offset, but emit a warning:
>
> [Firmware Bug]: Kernel image misaligned at boot, please fix your bootloader!
>
> To fix this properly, let's drop the seek operation altogether, instead
> give the kernel header parsing function a memory buffer, containing the
> first 64 bytes of the kernel file. We read the rest of the file into the
> right location after this function has decoded the proper kernel offset.
>
> This brings back proper loading even for kernels loaded via pipes.
are there any opinions on this?
Look, Marc, it's a negative diffstat ;-)
Cheers,
Andre
>
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> ---
> arm/aarch64/include/kvm/kvm-arch.h | 3 ++-
> arm/aarch64/kvm.c | 26 ++++++++------------------
> arm/kvm.c | 13 ++++++++++---
> 3 files changed, 20 insertions(+), 22 deletions(-)
>
> diff --git a/arm/aarch64/include/kvm/kvm-arch.h b/arm/aarch64/include/kvm/kvm-arch.h
> index 55ef8ed1..7e6cffb6 100644
> --- a/arm/aarch64/include/kvm/kvm-arch.h
> +++ b/arm/aarch64/include/kvm/kvm-arch.h
> @@ -2,7 +2,8 @@
> #define KVM__KVM_ARCH_H
>
> struct kvm;
> -unsigned long long kvm__arch_get_kern_offset(struct kvm *kvm, int fd);
> +unsigned long long kvm__arch_get_kern_offset(struct kvm *kvm, void *header,
> + unsigned int bufsize);
>
> #define ARM_MAX_MEMORY(kvm) ((kvm)->cfg.arch.aarch32_guest ? \
> ARM_LOMAP_MAX_MEMORY : \
> diff --git a/arm/aarch64/kvm.c b/arm/aarch64/kvm.c
> index 49e1dd31..9a6460ac 100644
> --- a/arm/aarch64/kvm.c
> +++ b/arm/aarch64/kvm.c
> @@ -10,39 +10,29 @@
> * instead of Little-Endian. BE kernels of this vintage may fail to
> * boot. See Documentation/arm64/booting.rst in your local kernel tree.
> */
> -unsigned long long kvm__arch_get_kern_offset(struct kvm *kvm, int fd)
> +unsigned long long kvm__arch_get_kern_offset(struct kvm *kvm,
> + void *buffer, unsigned int bufsize)
> {
> - struct arm64_image_header header;
> - off_t cur_offset;
> - ssize_t size;
> + struct arm64_image_header *header = buffer;
> const char *warn_str;
>
> /* the 32bit kernel offset is a well known value */
> if (kvm->cfg.arch.aarch32_guest)
> return 0x8000;
>
> - cur_offset = lseek(fd, 0, SEEK_CUR);
> - if (cur_offset == (off_t)-1 ||
> - lseek(fd, 0, SEEK_SET) == (off_t)-1) {
> - warn_str = "Failed to seek in kernel image file";
> + if (bufsize < sizeof(*header)) {
> + warn_str = "Provided kernel header too small";
> goto fail;
> }
>
> - size = xread(fd, &header, sizeof(header));
> - if (size < 0 || (size_t)size < sizeof(header))
> - die("Failed to read kernel image header");
> -
> - lseek(fd, cur_offset, SEEK_SET);
> -
> - if (memcmp(&header.magic, ARM64_IMAGE_MAGIC, sizeof(header.magic)))
> + if (memcmp(&header->magic, ARM64_IMAGE_MAGIC, sizeof(header->magic)))
> pr_warning("Kernel image magic not matching");
>
> - if (le64_to_cpu(header.image_size))
> - return le64_to_cpu(header.text_offset);
> + if (le64_to_cpu(header->image_size))
> + return le64_to_cpu(header->text_offset);
>
> warn_str = "Image size is 0";
> fail:
> pr_warning("%s, assuming TEXT_OFFSET to be 0x80000", warn_str);
> return 0x80000;
> }
> -
> diff --git a/arm/kvm.c b/arm/kvm.c
> index 5aea18fe..685fabb1 100644
> --- a/arm/kvm.c
> +++ b/arm/kvm.c
> @@ -90,12 +90,14 @@ void kvm__arch_init(struct kvm *kvm, const char *hugetlbfs_path, u64 ram_size)
>
> #define FDT_ALIGN SZ_2M
> #define INITRD_ALIGN 4
> +#define MAX_KERNEL_HEADER_SIZE 64
> bool kvm__arch_load_kernel_image(struct kvm *kvm, int fd_kernel, int fd_initrd,
> const char *kernel_cmdline)
> {
> void *pos, *kernel_end, *limit;
> unsigned long guest_addr;
> ssize_t file_size;
> + char header[MAX_KERNEL_HEADER_SIZE];
>
> /*
> * Linux requires the initrd and dtb to be mapped inside lowmem,
> @@ -103,16 +105,21 @@ bool kvm__arch_load_kernel_image(struct kvm *kvm, int fd_kernel, int fd_initrd,
> */
> limit = kvm->ram_start + min(kvm->ram_size, (u64)SZ_256M) - 1;
>
> - pos = kvm->ram_start + kvm__arch_get_kern_offset(kvm, fd_kernel);
> + if (xread(fd_kernel, header, sizeof(header)) != sizeof(header))
> + die_perror("kernel header read");
> + pos = kvm->ram_start + kvm__arch_get_kern_offset(kvm, header,
> + sizeof(header));
> kvm->arch.kern_guest_start = host_to_guest_flat(kvm, pos);
> - file_size = read_file(fd_kernel, pos, limit - pos);
> + memcpy(pos, header, sizeof(header));
> + file_size = read_file(fd_kernel, pos + sizeof(header),
> + limit - pos - sizeof(header));
> if (file_size < 0) {
> if (errno == ENOMEM)
> die("kernel image too big to contain in guest memory.");
>
> die_perror("kernel read");
> }
> - kernel_end = pos + file_size;
> + kernel_end = pos + file_size + sizeof(header);
> pr_debug("Loaded kernel to 0x%llx (%zd bytes)",
> kvm->arch.kern_guest_start, file_size);
>
>
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