Commit message: x86/microcode/intel: Guard against stack overflow in the loader

mc_saved_tmp is a static array allocated on the stack, we need to make
sure mc_saved_count stays within its bounds, otherwise we're overflowing
the stack in _save_mc(). A specially crafted microcode header could lead
to a kernel crash or potentially kernel execution.

Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1422964824-22056-1-git-send-email-quentin.casasnovas@oracle.com
Signed-off-by: Borislav Petkov <bp@suse.de>
CVE: CVE-2015-2666
CWE: CWE-119
Vulnerability description: Stack-based buffer overflow in the get_matching_model_microcode function in arch/x86/kernel/cpu/microcode/intel_early.c in the Linux kernel before 4.0 allows context-dependent attackers to gain privileges by constructing a crafted microcode header and leveraging root privileges for write access to the initrd.

Project: linux
File: intel_early.c

_load_ucode_intel_bsp(struct mc_saved_data *mc_saved_data,
		      unsigned long *mc_saved_in_initrd,
		      unsigned long initrd_start_early,
		      unsigned long initrd_end_early,
		      struct ucode_cpu_info *uci)
{
	enum ucode_state ret;

	collect_cpu_info_early(uci);
	scan_microcode(initrd_start_early, initrd_end_early, mc_saved_data,
		       mc_saved_in_initrd, uci);

	ret = load_microcode(mc_saved_data, mc_saved_in_initrd,
			     initrd_start_early, uci);

	if (ret == UCODE_OK)
		apply_microcode_early(uci, true);
}

Project: linux
File: intel_early.c

static void _save_mc(struct microcode_intel **mc_saved, u8 *ucode_ptr,
		     unsigned int *mc_saved_count_p)
{
	int i;
	int found = 0;
	unsigned int mc_saved_count = *mc_saved_count_p;
	struct microcode_header_intel *mc_header;

	mc_header = (struct microcode_header_intel *)ucode_ptr;
	for (i = 0; i < mc_saved_count; i++) {
		unsigned int sig, pf;
		unsigned int new_rev;
		struct microcode_header_intel *mc_saved_header =
			     (struct microcode_header_intel *)mc_saved[i];
		sig = mc_saved_header->sig;
		pf = mc_saved_header->pf;
		new_rev = mc_header->rev;

		if (get_matching_sig(sig, pf, ucode_ptr, new_rev)) {
			found = 1;
			if (update_match_revision(mc_header, new_rev)) {
				/*
				 * Found an older ucode saved before.
				 * Replace the older one with this newer
				 * one.
				 */
				mc_saved[i] =
					(struct microcode_intel *)ucode_ptr;
				break;
			}
		}
	}
	if (i >= mc_saved_count && !found)
		/*
		 * This ucode is first time discovered in ucode file.
		 * Save it to memory.
		 */
		mc_saved[mc_saved_count++] =
				 (struct microcode_intel *)ucode_ptr;

	*mc_saved_count_p = mc_saved_count;
}

Project: linux
File: intel_early.c

static int apply_microcode_early(struct ucode_cpu_info *uci, bool early)
{
	struct microcode_intel *mc_intel;
	unsigned int val[2];

	mc_intel = uci->mc;
	if (mc_intel == NULL)
		return 0;

	/* write microcode via MSR 0x79 */
	native_wrmsr(MSR_IA32_UCODE_WRITE,
	      (unsigned long) mc_intel->bits,
	      (unsigned long) mc_intel->bits >> 16 >> 16);
	native_wrmsr(MSR_IA32_UCODE_REV, 0, 0);

	/* As documented in the SDM: Do a CPUID 1 here */
	sync_core();

	/* get the current revision from MSR 0x8B */
	native_rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);
	if (val[1] != mc_intel->hdr.rev)
		return -1;

#ifdef CONFIG_X86_64
	/* Flush global tlb. This is precaution. */
	flush_tlb_early();
#endif
	uci->cpu_sig.rev = val[1];

	if (early)
		print_ucode(uci);
	else
		print_ucode_info(uci, mc_intel->hdr.date);

	return 0;
}

Project: linux
File: intel_early.c

static inline void flush_tlb_early(void)
{
	__native_flush_tlb_global_irq_disabled();
}

Project: linux
File: intel_early.c

generic_load_microcode_early(struct microcode_intel **mc_saved_p,
			     unsigned int mc_saved_count,
			     struct ucode_cpu_info *uci)
{
	struct microcode_intel *ucode_ptr, *new_mc = NULL;
	int new_rev = uci->cpu_sig.rev;
	enum ucode_state state = UCODE_OK;
	unsigned int mc_size;
	struct microcode_header_intel *mc_header;
	unsigned int csig = uci->cpu_sig.sig;
	unsigned int cpf = uci->cpu_sig.pf;
	int i;

	for (i = 0; i < mc_saved_count; i++) {
		ucode_ptr = mc_saved_p[i];

		mc_header = (struct microcode_header_intel *)ucode_ptr;
		mc_size = get_totalsize(mc_header);
		if (get_matching_microcode(csig, cpf, ucode_ptr, new_rev)) {
			new_rev = mc_header->rev;
			new_mc  = ucode_ptr;
		}
	}

	if (!new_mc) {
		state = UCODE_NFOUND;
		goto out;
	}

	uci->mc = (struct microcode_intel *)new_mc;
out:
	return state;
}

Project: linux
File: intel_early.c

static u8 get_x86_family(unsigned long sig)
{
	u8 x86;

	x86 = (sig >> 8) & 0xf;

	if (x86 == 0xf)
		x86 += (sig >> 20) & 0xff;

	return x86;
}

Project: linux
File: intel_early.c

static u8 get_x86_model(unsigned long sig)
{
	u8 x86, x86_model;

	x86 = get_x86_family(sig);
	x86_model = (sig >> 4) & 0xf;

	if (x86 == 0x6 || x86 == 0xf)
		x86_model += ((sig >> 16) & 0xf) << 4;

	return x86_model;
}

Project: linux
File: intel_early.c

load_microcode(struct mc_saved_data *mc_saved_data,
	       unsigned long *mc_saved_in_initrd,
	       unsigned long initrd_start,
	       struct ucode_cpu_info *uci)
{
	struct microcode_intel *mc_saved_tmp[MAX_UCODE_COUNT];
	unsigned int count = mc_saved_data->mc_saved_count;

	if (!mc_saved_data->mc_saved) {
		microcode_pointer(mc_saved_tmp, mc_saved_in_initrd,
				  initrd_start, count);

		return generic_load_microcode_early(mc_saved_tmp, count, uci);
	} else {
#ifdef CONFIG_X86_32
		microcode_phys(mc_saved_tmp, mc_saved_data);
		return generic_load_microcode_early(mc_saved_tmp, count, uci);
#else
		return generic_load_microcode_early(mc_saved_data->mc_saved,
						    count, uci);
#endif
	}
}

Project: linux
File: intel_early.c

void load_ucode_intel_ap(void)
{
	struct mc_saved_data *mc_saved_data_p;
	struct ucode_cpu_info uci;
	unsigned long *mc_saved_in_initrd_p;
	unsigned long initrd_start_addr;
#ifdef CONFIG_X86_32
	unsigned long *initrd_start_p;

	mc_saved_in_initrd_p =
		(unsigned long *)__pa_nodebug(mc_saved_in_initrd);
	mc_saved_data_p = (struct mc_saved_data *)__pa_nodebug(&mc_saved_data);
	initrd_start_p = (unsigned long *)__pa_nodebug(&initrd_start);
	initrd_start_addr = (unsigned long)__pa_nodebug(*initrd_start_p);
#else
	mc_saved_data_p = &mc_saved_data;
	mc_saved_in_initrd_p = mc_saved_in_initrd;
	initrd_start_addr = initrd_start;
#endif

	/*
	 * If there is no valid ucode previously saved in memory, no need to
	 * update ucode on this AP.
	 */
	if (mc_saved_data_p->mc_saved_count == 0)
		return;

	collect_cpu_info_early(&uci);
	load_microcode(mc_saved_data_p, mc_saved_in_initrd_p,
		       initrd_start_addr, &uci);
	apply_microcode_early(&uci, true);
}

Project: linux
File: intel_early.c

load_ucode_intel_bsp(void)
{
	u64 ramdisk_image, ramdisk_size;
	unsigned long initrd_start_early, initrd_end_early;
	struct ucode_cpu_info uci;
#ifdef CONFIG_X86_32
	struct boot_params *boot_params_p;

	boot_params_p = (struct boot_params *)__pa_nodebug(&boot_params);
	ramdisk_image = boot_params_p->hdr.ramdisk_image;
	ramdisk_size  = boot_params_p->hdr.ramdisk_size;
	initrd_start_early = ramdisk_image;
	initrd_end_early = initrd_start_early + ramdisk_size;

	_load_ucode_intel_bsp(
		(struct mc_saved_data *)__pa_nodebug(&mc_saved_data),
		(unsigned long *)__pa_nodebug(&mc_saved_in_initrd),
		initrd_start_early, initrd_end_early, &uci);
#else
	ramdisk_image = boot_params.hdr.ramdisk_image;
	ramdisk_size  = boot_params.hdr.ramdisk_size;
	initrd_start_early = ramdisk_image + PAGE_OFFSET;
	initrd_end_early = initrd_start_early + ramdisk_size;

	_load_ucode_intel_bsp(&mc_saved_data, mc_saved_in_initrd,
			      initrd_start_early, initrd_end_early,
			      &uci);
#endif
}

Project: linux
File: intel_early.c

microcode_phys(struct microcode_intel **mc_saved_tmp,
	       struct mc_saved_data *mc_saved_data)
{
	int i;
	struct microcode_intel ***mc_saved;

	mc_saved = (struct microcode_intel ***)
		   __pa_nodebug(&mc_saved_data->mc_saved);
	for (i = 0; i < mc_saved_data->mc_saved_count; i++) {
		struct microcode_intel *p;

		p = *(struct microcode_intel **)
			__pa_nodebug(mc_saved_data->mc_saved + i);
		mc_saved_tmp[i] = (struct microcode_intel *)__pa_nodebug(p);
	}
}

Project: linux
File: intel_early.c

microcode_pointer(struct microcode_intel **mc_saved,
		  unsigned long *mc_saved_in_initrd,
		  unsigned long initrd_start, int mc_saved_count)
{
	int i;

	for (i = 0; i < mc_saved_count; i++)
		mc_saved[i] = (struct microcode_intel *)
			      (mc_saved_in_initrd[i] + initrd_start);
}

Project: linux
File: intel_early.c

static void print_ucode(struct ucode_cpu_info *uci)
{
	struct microcode_intel *mc_intel;
	int *delay_ucode_info_p;
	int *current_mc_date_p;

	mc_intel = uci->mc;
	if (mc_intel == NULL)
		return;

	delay_ucode_info_p = (int *)__pa_nodebug(&delay_ucode_info);
	current_mc_date_p = (int *)__pa_nodebug(&current_mc_date);

	*delay_ucode_info_p = 1;
	*current_mc_date_p = mc_intel->hdr.date;
}

Project: linux
File: intel_early.c

print_ucode_info(struct ucode_cpu_info *uci, unsigned int date)
{
	int cpu = smp_processor_id();

	pr_info("CPU%d microcode updated early to revision 0x%x, date = %04x-%02x-%02x\n",
		cpu,
		uci->cpu_sig.rev,
		date & 0xffff,
		date >> 24,
		(date >> 16) & 0xff);
}

Project: linux
File: intel_early.c

void reload_ucode_intel(void)
{
	struct ucode_cpu_info uci;
	enum ucode_state ret;

	if (!mc_saved_data.mc_saved_count)
		return;

	collect_cpu_info_early(&uci);

	ret = generic_load_microcode_early(mc_saved_data.mc_saved,
					   mc_saved_data.mc_saved_count, &uci);
	if (ret != UCODE_OK)
		return;

	apply_microcode_early(&uci, false);
}

Project: linux
File: intel_early.c

save_microcode(struct mc_saved_data *mc_saved_data,
	       struct microcode_intel **mc_saved_src,
	       unsigned int mc_saved_count)
{
	int i, j;
	struct microcode_intel **mc_saved_p;
	int ret;

	if (!mc_saved_count)
		return -EINVAL;

	/*
	 * Copy new microcode data.
	 */
	mc_saved_p = kmalloc(mc_saved_count*sizeof(struct microcode_intel *),
			     GFP_KERNEL);
	if (!mc_saved_p)
		return -ENOMEM;

	for (i = 0; i < mc_saved_count; i++) {
		struct microcode_intel *mc = mc_saved_src[i];
		struct microcode_header_intel *mc_header = &mc->hdr;
		unsigned long mc_size = get_totalsize(mc_header);
		mc_saved_p[i] = kmalloc(mc_size, GFP_KERNEL);
		if (!mc_saved_p[i]) {
			ret = -ENOMEM;
			goto err;
		}
		if (!mc_saved_src[i]) {
			ret = -EINVAL;
			goto err;
		}
		memcpy(mc_saved_p[i], mc, mc_size);
	}

	/*
	 * Point to newly saved microcode.
	 */
	mc_saved_data->mc_saved = mc_saved_p;
	mc_saved_data->mc_saved_count = mc_saved_count;

	return 0;

err:
	for (j = 0; j <= i; j++)
		kfree(mc_saved_p[j]);
	kfree(mc_saved_p);

	return ret;
}

Project: linux
File: intel_early.c

int __init save_microcode_in_initrd_intel(void)
{
	unsigned int count = mc_saved_data.mc_saved_count;
	struct microcode_intel *mc_saved[MAX_UCODE_COUNT];
	int ret = 0;

	if (count == 0)
		return ret;

	microcode_pointer(mc_saved, mc_saved_in_initrd, initrd_start, count);
	ret = save_microcode(&mc_saved_data, mc_saved, count);
	if (ret)
		pr_err("Cannot save microcode patches from initrd.\n");

	show_saved_mc();

	return ret;
}

Project: linux
File: intel_early.c

scan_microcode(unsigned long start, unsigned long end,
		struct mc_saved_data *mc_saved_data,
		unsigned long *mc_saved_in_initrd,
		struct ucode_cpu_info *uci)
{
	unsigned int size = end - start + 1;
	struct cpio_data cd;
	long offset = 0;
#ifdef CONFIG_X86_32
	char *p = (char *)__pa_nodebug(ucode_name);
#else
	char *p = ucode_name;
#endif

	cd.data = NULL;
	cd.size = 0;

	cd = find_cpio_data(p, (void *)start, size, &offset);
	if (!cd.data)
		return UCODE_ERROR;


	return get_matching_model_microcode(0, start, cd.data, cd.size,
					    mc_saved_data, mc_saved_in_initrd,
					    uci);
}

Project: linux
File: intel_early.c

static void __ref show_saved_mc(void)
{
	int i, j;
	unsigned int sig, pf, rev, total_size, data_size, date;
	struct ucode_cpu_info uci;

	if (mc_saved_data.mc_saved_count == 0) {
		pr_debug("no microcode data saved.\n");
		return;
	}
	pr_debug("Total microcode saved: %d\n", mc_saved_data.mc_saved_count);

	collect_cpu_info_early(&uci);

	sig = uci.cpu_sig.sig;
	pf = uci.cpu_sig.pf;
	rev = uci.cpu_sig.rev;
	pr_debug("CPU%d: sig=0x%x, pf=0x%x, rev=0x%x\n",
		 smp_processor_id(), sig, pf, rev);

	for (i = 0; i < mc_saved_data.mc_saved_count; i++) {
		struct microcode_header_intel *mc_saved_header;
		struct extended_sigtable *ext_header;
		int ext_sigcount;
		struct extended_signature *ext_sig;

		mc_saved_header = (struct microcode_header_intel *)
				  mc_saved_data.mc_saved[i];
		sig = mc_saved_header->sig;
		pf = mc_saved_header->pf;
		rev = mc_saved_header->rev;
		total_size = get_totalsize(mc_saved_header);
		data_size = get_datasize(mc_saved_header);
		date = mc_saved_header->date;

		pr_debug("mc_saved[%d]: sig=0x%x, pf=0x%x, rev=0x%x, toal size=0x%x, date = %04x-%02x-%02x\n",
			 i, sig, pf, rev, total_size,
			 date & 0xffff,
			 date >> 24,
			 (date >> 16) & 0xff);

		/* Look for ext. headers: */
		if (total_size <= data_size + MC_HEADER_SIZE)
			continue;

		ext_header = (struct extended_sigtable *)
			     mc_saved_header + data_size + MC_HEADER_SIZE;
		ext_sigcount = ext_header->count;
		ext_sig = (void *)ext_header + EXT_HEADER_SIZE;

		for (j = 0; j < ext_sigcount; j++) {
			sig = ext_sig->sig;
			pf = ext_sig->pf;

			pr_debug("\tExtended[%d]: sig=0x%x, pf=0x%x\n",
				 j, sig, pf);

			ext_sig++;
		}

	}
}

Project: linux
File: intel_early.c

static inline void show_saved_mc(void)
{
}

Project: linux
File: intel_early.c

void show_ucode_info_early(void)
{
	struct ucode_cpu_info uci;

	if (delay_ucode_info) {
		collect_cpu_info_early(&uci);
		print_ucode_info(&uci, current_mc_date);
		delay_ucode_info = 0;
	}
}