Re: [PATCH 11/13] kexec-bzImage: Support for loading bzImage using 64bit entry

Borislav Petkov
2014-06-15T16:35:34Z

On Tue, Jun 03, 2014 at 09:07:00AM -0400, Vivek Goyal wrote:
> This is loader specific code which can load bzImage and set it up for
> 64bit entry. This does not take care of 32bit entry or real mode entry.
>
> 32bit mode entry can be implemented if somebody needs it.
>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> ---

...

> diff --git a/arch/x86/kernel/kexec-bzimage.c b/arch/x86/kernel/kexec-bzimage.c
> new file mode 100644
> index 0000000..0750784
> --- /dev/null
> +++ b/arch/x86/kernel/kexec-bzimage.c
> @@ -0,0 +1,269 @@
> +/*
> + * Kexec bzImage loader
> + *
> + * Copyright (C) 2014 Red Hat Inc.
> + * Authors:
> + * Vivek Goyal <vgoyal@redhat.com>
> + *
> + * This source code is licensed under the GNU General Public License,
> + * Version 2. See the file COPYING for more details.
> + */
> +#include <linux/string.h>
> +#include <linux/printk.h>
> +#include <linux/errno.h>
> +#include <linux/slab.h>
> +#include <linux/kexec.h>
> +#include <linux/kernel.h>
> +#include <linux/mm.h>
> +
> +#include <asm/bootparam.h>
> +#include <asm/setup.h>
> +
> +/*
> + * Defines lowest physical address for various segments. Not sure where
> + * exactly these limits came from. Current bzimage64 loader in kexec-tools
> + * uses these so I am retaining it. It can be changed over time as we gain
> + * more insight.
> + */
> +#define MIN_PURGATORY_ADDR 0x3000
> +#define MIN_BOOTPARAM_ADDR 0x3000
> +#define MIN_KERNEL_LOAD_ADDR 0x100000
> +#define MIN_INITRD_LOAD_ADDR 0x1000000
> +
> +#ifdef CONFIG_X86_64
> +
> +/*
> + * This is a place holder for all boot loader specific data structure which
> + * gets allocated in one call but gets freed much later during cleanup
> + * time. Right now there is only one field but it can grow as need be.
> + */
> +struct bzimage64_data {
> + /*
> + * Temporary buffer to hold bootparams buffer. This should be
> + * freed once the bootparam segment has been loaded.
> + */
> + void *bootparams_buf;
> +};
> +
> +int bzImage64_probe(const char *buf, unsigned long len)
> +{
> + int ret = -ENOEXEC;
> + struct setup_header *header;
> +
> + /* kernel should be atleast two sector long */

two sectors

> + if (len < 2 * 512) {
> + pr_debug("File is too short to be a bzImage\n");

Those error messages are all pr_debug. Now, wouldn't we want to tell
userspace what the problem is, *when* there is one?

I.e., pr_err or pr_info is much more helpful than pr_debug IMO.

> + return ret;
> + }
> +
> + header = (struct setup_header *)(buf + offsetof(struct boot_params,
> + hdr));

Just let that stick out. The 80 cols limit is not a hard one anyway,
especially if it impairs readability.

> + if (memcmp((char *)&header->header, "HdrS", 4) != 0) {

Not strncmp? "HdrS" is a string...

> + pr_debug("Not a bzImage\n");
> + return ret;
> + }
> +
> + if (header->boot_flag != 0xAA55) {
> + pr_debug("No x86 boot sector present\n");
> + return ret;
> + }
> +
> + if (header->version < 0x020C) {
> + pr_debug("Must be at least protocol version 2.12\n");
> + return ret;
> + }
> +
> + if ((header->loadflags & LOADED_HIGH) == 0) {

if (!(header->loadflags.. ))

> + pr_debug("zImage not a bzImage\n");
> + return ret;
> + }
> +
> + if (!(header->xloadflags & XLF_KERNEL_64)) {
> + pr_debug("Not a bzImage64. XLF_KERNEL_64 is not set.\n");
> + return ret;
> + }
> +
> + if (!(header->xloadflags & XLF_CAN_BE_LOADED_ABOVE_4G)) {
> + pr_debug("XLF_CAN_BE_LOADED_ABOVE_4G is not set.\n");
> + return ret;
> + }

Just merge the two checks:

if ((header->xloadflags & (XLF_KERNEL_64 | XLF_CAN_BE_LOADED_ABOVE_4G)) !=
(XLF_KERNEL_64 | XLF_CAN_BE_LOADED_ABOVE_4G)) {
pr_err("Not a bzImage, xloadflags: 0x%x\n", header->xloadflags);
return ret;
}

> +
> + /* I've got a bzImage */
> + pr_debug("It's a relocatable bzImage64\n");
> + ret = 0;
> +
> + return ret;
> +}
> +
> +void *bzImage64_load(struct kimage *image, char *kernel,
> + unsigned long kernel_len,
> + char *initrd, unsigned long initrd_len,
> + char *cmdline, unsigned long cmdline_len)

Arg alignment.

> +{
> +
> + struct setup_header *header;
> + int setup_sects, kern16_size, ret = 0;
> + unsigned long setup_header_size, params_cmdline_sz;
> + struct boot_params *params;
> + unsigned long bootparam_load_addr, kernel_load_addr, initrd_load_addr;
> + unsigned long purgatory_load_addr;
> + unsigned long kernel_bufsz, kernel_memsz, kernel_align;
> + char *kernel_buf;
> + struct bzimage64_data *ldata;
> + struct kexec_entry64_regs regs64;
> + void *stack;
> + unsigned int setup_hdr_offset = offsetof(struct boot_params, hdr);
> +
> + header = (struct setup_header *)(kernel + setup_hdr_offset);
> + setup_sects = header->setup_sects;
> + if (setup_sects == 0)
> + setup_sects = 4;
> +
> + kern16_size = (setup_sects + 1) * 512;
> + if (kernel_len < kern16_size) {
> + pr_debug("bzImage truncated\n");

Ditto for all those pr_debug's in here - I think we want to know why the
bzImage load fails and pr_debug is not suitable for that.

> + return ERR_PTR(-ENOEXEC);
> + }
> +
> + if (cmdline_len > header->cmdline_size) {

As we talked, I think COMMAND_LINE_SIZE is perfectly fine and safe for
all intents and purposes.

> + pr_debug("Kernel command line too long\n");
> + return ERR_PTR(-EINVAL);
> + }
> +
> + /* Allocate loader specific data */
> + ldata = kzalloc(sizeof(struct bzimage64_data), GFP_KERNEL);
> + if (!ldata)
> + return ERR_PTR(-ENOMEM);

Why don't you move that allocation to the place right before it is being
assigned to it? I.e., to the "ldata->bootparams_buf = params" line.

This way you'll save yourself all the goto games on the error path and
do it only after everything else has succeeded.

> +
> + /*
> + * Load purgatory. For 64bit entry point, purgatory code can be
> + * anywhere.
> + */
> + ret = kexec_load_purgatory(image, MIN_PURGATORY_ADDR, ULONG_MAX, 1,
> + &purgatory_load_addr);
> + if (ret) {
> + pr_debug("Loading purgatory failed\n");
> + goto out_free_loader_data;
> + }
> +
> + pr_debug("Loaded purgatory at 0x%lx\n", purgatory_load_addr);
> +
> + /* Load Bootparams and cmdline */
> + params_cmdline_sz = sizeof(struct boot_params) + cmdline_len;
> + params = kzalloc(params_cmdline_sz, GFP_KERNEL);
> + if (!params) {
> + ret = -ENOMEM;
> + goto out_free_loader_data;
> + }
> +
> + /* Copy setup header onto bootparams. Documentation/x86/boot.txt */
> + setup_header_size = 0x0202 + kernel[0x0201] - setup_hdr_offset;
> +
> + /* Is there a limit on setup header size? */
> + memcpy(&params->hdr, (kernel + setup_hdr_offset), setup_header_size);
> +
> + ret = kexec_add_buffer(image, (char *)params, params_cmdline_sz,
> + params_cmdline_sz, 16, MIN_BOOTPARAM_ADDR,
> + ULONG_MAX, 1, &bootparam_load_addr);
> + if (ret)
> + goto out_free_params;
> + pr_debug("Loaded boot_param and command line at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
> + bootparam_load_addr, params_cmdline_sz, params_cmdline_sz);
> +
> + /* Load kernel */
> + kernel_buf = kernel + kern16_size;
> + kernel_bufsz = kernel_len - kern16_size;
> + kernel_memsz = ALIGN(header->init_size, 4096);

PAGE_ALIGN

> + kernel_align = header->kernel_alignment;
> +
> + ret = kexec_add_buffer(image, kernel_buf,
> + kernel_bufsz, kernel_memsz, kernel_align,
> + MIN_KERNEL_LOAD_ADDR, ULONG_MAX, 1,
> + &kernel_load_addr);
> + if (ret)
> + goto out_free_params;
> +
> + pr_debug("Loaded 64bit kernel at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
> + kernel_load_addr, kernel_memsz, kernel_memsz);
> +
> + /* Load initrd high */
> + if (initrd) {
> + ret = kexec_add_buffer(image, initrd, initrd_len, initrd_len,
> + PAGE_SIZE, MIN_INITRD_LOAD_ADDR,
> + ULONG_MAX, 1, &initrd_load_addr);
> + if (ret)
> + goto out_free_params;
> +
> + pr_debug("Loaded initrd at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
> + initrd_load_addr, initrd_len, initrd_len);

emtpy line to split, pls.

> + ret = kexec_setup_initrd(params, initrd_load_addr, initrd_len);
> + if (ret)

This ret is unconditionally 0 - no need to check it.

> + goto out_free_params;
> + }
> +
> + ret = kexec_setup_cmdline(params, bootparam_load_addr,
> + sizeof(struct boot_params), cmdline,
> + cmdline_len);
> + if (ret)

Ditto.

> + goto out_free_params;
> +
> + /* bootloader info. Do we need a separate ID for kexec kernel loader? */
> + params->hdr.type_of_loader = 0x0D << 4;
> + params->hdr.loadflags = 0;
> +
> + /* Setup purgatory regs for entry */
> + ret = kexec_purgatory_get_set_symbol(image, "entry64_regs", &regs64,
> + sizeof(regs64), 1);
> + if (ret)
> + goto out_free_params;
> +
> + regs64.rbx = 0; /* Bootstrap Processor */
> + regs64.rsi = bootparam_load_addr;
> + regs64.rip = kernel_load_addr + 0x200;
> + stack = kexec_purgatory_get_symbol_addr(image, "stack_end");
> + if (IS_ERR(stack)) {
> + pr_debug("Could not find address of symbol stack_end\n");
> + ret = -EINVAL;
> + goto out_free_params;
> + }
> +
> + regs64.rsp = (unsigned long)stack;
> + ret = kexec_purgatory_get_set_symbol(image, "entry64_regs", &regs64,
> + sizeof(regs64), 0);
> + if (ret)
> + goto out_free_params;
> +
> + ret = kexec_setup_boot_parameters(params);

Ditto.

> + if (ret)
> + goto out_free_params;
> +
> + /*
> + * Store pointer to params so that it could be freed after loading
> + * params segment has been loaded and contents have been copied
> + * somewhere else.
> + */
> + ldata->bootparams_buf = params;
> + return ldata;
> +
> +out_free_params:
> + kfree(params);
> +out_free_loader_data:
> + kfree(ldata);
> + return ERR_PTR(ret);
> +}
> +
> +/* This cleanup function is called after various segments have been loaded */
> +int bzImage64_cleanup(struct kimage *image)
> +{
> + struct bzimage64_data *ldata = image->image_loader_data;
> +
> + if (!ldata)
> + return 0;
> +
> + kfree(ldata->bootparams_buf);
> + ldata->bootparams_buf = NULL;
> +
> + return 0;
> +}
> +
> +#endif /* CONFIG_X86_64 */
> diff --git a/arch/x86/kernel/machine_kexec.c b/arch/x86/kernel/machine_kexec.c
> new file mode 100644
> index 0000000..7de3239
> --- /dev/null
> +++ b/arch/x86/kernel/machine_kexec.c
> @@ -0,0 +1,136 @@
> +/*
> + * handle transition of Linux booting another kernel
> + *
> + * Copyright (C) 2014 Red Hat Inc.
> + * Authors:
> + * Vivek Goyal <vgoyal@redhat.com>
> + *
> + * This source code is licensed under the GNU General Public License,
> + * Version 2. See the file COPYING for more details.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/string.h>
> +#include <asm/bootparam.h>
> +#include <asm/setup.h>
> +
> +/*
> + * Common code for x86 and x86_64 used for kexec.
> + *
> + * For the time being it compiles only for x86_64 as there are no image
> + * loaders implemented * for x86. This #ifdef can be removed once somebody
> + * decides to write an image loader on CONFIG_X86_32.
> + */
> +
> +#ifdef CONFIG_X86_64

Ok, this doesn't make any sense: this new machine_kexec.c is supposed to
be common code and yet it has this 64-bit ifdef in there.

It should be the other way around, IMO: put it now in machine_kexec_64.c
and if someone wants the 32-bit version, that someone should carve it
out. This'll save you the needless ifdeffery now.

> +
> +int kexec_setup_initrd(struct boot_params *params,
> + unsigned long initrd_load_addr, unsigned long initrd_len)
> +{
> + params->hdr.ramdisk_image = initrd_load_addr & 0xffffffffUL;
> + params->hdr.ramdisk_size = initrd_len & 0xffffffffUL;

We have more readable GENMASK* macros for contiguous masks. This one
will then look like:

params->hdr.ramdisk_image = initrd_load_addr & GENMASK(31, 0);
params->hdr.ramdisk_size = initrd_len & GENMASK(31, 0);

and this way we know exactly about which bits are we talking about. :)

> +
> + params->ext_ramdisk_image = initrd_load_addr >> 32;
> + params->ext_ramdisk_size = initrd_len >> 32;
> +
> + return 0;
> +}
> +
> +int kexec_setup_cmdline(struct boot_params *params,
> + unsigned long bootparams_load_addr,
> + unsigned long cmdline_offset, char *cmdline,
> + unsigned long cmdline_len)
> +{
> + char *cmdline_ptr = ((char *)params) + cmdline_offset;
> + unsigned long cmdline_ptr_phys;
> + uint32_t cmdline_low_32, cmdline_ext_32;
> +
> + memcpy(cmdline_ptr, cmdline, cmdline_len);
> + cmdline_ptr[cmdline_len - 1] = '\0';
> +
> + cmdline_ptr_phys = bootparams_load_addr + cmdline_offset;
> + cmdline_low_32 = cmdline_ptr_phys & 0xffffffffUL;

GENMASK

> + cmdline_ext_32 = cmdline_ptr_phys >> 32;
> +
> + params->hdr.cmd_line_ptr = cmdline_low_32;
> + if (cmdline_ext_32)
> + params->ext_cmd_line_ptr = cmdline_ext_32;
> +
> + return 0;
> +}
> +
> +static int setup_memory_map_entries(struct boot_params *params)
> +{
> + unsigned int nr_e820_entries;
> +
> + /* TODO: What about EFI */

You're removing this line in 13/13 so don't add it at all... ?

> + nr_e820_entries = e820_saved.nr_map;
> + if (nr_e820_entries > E820MAX)
> + nr_e820_entries = E820MAX;
> +
> + params->e820_entries = nr_e820_entries;
> + memcpy(&params->e820_map, &e820_saved.map,
> + nr_e820_entries * sizeof(struct e820entry));
> +
> + return 0;
> +}
> +
> +int kexec_setup_boot_parameters(struct boot_params *params)
> +{
> + unsigned int nr_e820_entries;
> + unsigned long long mem_k, start, end;
> + int i;
> +
> + /* Get subarch from existing bootparams */
> + params->hdr.hardware_subarch = boot_params.hdr.hardware_subarch;
> +
> + /* Copying screen_info will do? */
> + memcpy(&params->screen_info, &boot_params.screen_info,
> + sizeof(struct screen_info));
> +
> + /* Fill in memsize later */
> + params->screen_info.ext_mem_k = 0;
> + params->alt_mem_k = 0;
> +
> + /* Default APM info */
> + memset(&params->apm_bios_info, 0, sizeof(params->apm_bios_info));
> +
> + /* Default drive info */
> + memset(&params->hd0_info, 0, sizeof(params->hd0_info));
> + memset(&params->hd1_info, 0, sizeof(params->hd1_info));
> +
> + /* Default sysdesc table */
> + params->sys_desc_table.length = 0;
> +
> + setup_memory_map_entries(params);
> + nr_e820_entries = params->e820_entries;
> +
> + for (i = 0; i < nr_e820_entries; i++) {
> + if (params->e820_map[i].type != E820_RAM)
> + continue;
> + start = params->e820_map[i].addr;
> + end = params->e820_map[i].addr + params->e820_map[i].size - 1;
> +
> + if ((start <= 0x100000) && end > 0x100000) {
> + mem_k = (end >> 10) - (0x100000 >> 10);
> + params->screen_info.ext_mem_k = mem_k;
> + params->alt_mem_k = mem_k;
> + if (mem_k > 0xfc00)
> + params->screen_info.ext_mem_k = 0xfc00; /* 64M*/
> + if (mem_k > 0xffffffff)
> + params->alt_mem_k = 0xffffffff;
> + }
> + }
> +
> + /* Setup EDD info */
> + memcpy(params->eddbuf, boot_params.eddbuf,
> + EDDMAXNR * sizeof(struct edd_info));
^^^^^^^^^^^^^^

Shouldn't you just copy eddbuf_entries many instead of EDDMAXNR?

> + params->eddbuf_entries = boot_params.eddbuf_entries;
> +

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
--