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2023-12-09 b22da3d8526a935aa31e086e63f60ff3246cb61c

 kernel/drivers/char/mem.c
..
..
@@ -29,13 +29,17 @@
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 #include <linux/export.h>
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 #include <linux/io.h>
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 #include <linux/uio.h>
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-
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 #include <linux/uaccess.h>
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+#include <linux/security.h>
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+#include <linux/pseudo_fs.h>
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+#include <uapi/linux/magic.h>
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+#include <linux/mount.h>
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37
 
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 #ifdef CONFIG_IA64
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 # include <linux/efi.h>
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 #endif
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41
 
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+#define DEVMEM_MINOR	1
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 #define DEVPORT_MINOR	4
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44
 
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 static inline unsigned long size_inside_page(unsigned long start,
..
..
@@ -167,7 +171,7 @@
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 			if (!ptr)
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 				goto failed;
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173
 
170
-			probe = probe_kernel_read(bounce, ptr, sz);
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+			probe = copy_from_kernel_nofault(bounce, ptr, sz);
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 			unxlate_dev_mem_ptr(p, ptr);
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 			if (probe)
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 				goto failed;
..
..
@@ -630,7 +634,7 @@
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 	unsigned long i = *ppos;
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 	char __user *tmp = buf;
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636
 
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-	if (!access_ok(VERIFY_WRITE, buf, count))
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+	if (!access_ok(buf, count))
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 		return -EFAULT;
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 	while (count-- > 0 && i < 65536) {
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 		if (__put_user(inb(i), tmp) < 0)
..
..
@@ -648,7 +652,7 @@
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 	unsigned long i = *ppos;
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 	const char __user *tmp = buf;
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654
 
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-	if (!access_ok(VERIFY_READ, buf, count))
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+	if (!access_ok(buf, count))
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 		return -EFAULT;
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 	while (count-- > 0 && i < 65536) {
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658
 		char c;
..
..
@@ -722,6 +726,33 @@
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 	return written;
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727
 }
724
728
 
729
+static ssize_t read_zero(struct file *file, char __user *buf,
730
+			 size_t count, loff_t *ppos)
731
+{
732
+	size_t cleared = 0;
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+
734
+	while (count) {
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+		size_t chunk = min_t(size_t, count, PAGE_SIZE);
736
+		size_t left;
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+
738
+		left = clear_user(buf + cleared, chunk);
739
+		if (unlikely(left)) {
740
+			cleared += (chunk - left);
741
+			if (!cleared)
742
+				return -EFAULT;
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+			break;
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+		}
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+		cleared += chunk;
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+		count -= chunk;
747
+
748
+		if (signal_pending(current))
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+			break;
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+		cond_resched();
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+	}
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+
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+	return cleared;
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+}
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+
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 static int mmap_zero(struct file *file, struct vm_area_struct *vma)
726
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 {
727
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 #ifndef CONFIG_MMU
..
..
@@ -787,7 +818,7 @@
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 	switch (orig) {
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819
 	case SEEK_CUR:
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 		offset += file->f_pos;
790
-		/* fall through */
821
+		fallthrough;
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822
 	case SEEK_SET:
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823
 		/* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
793
824
 		if ((unsigned long long)offset >= -MAX_ERRNO) {
..
..
@@ -805,9 +836,65 @@
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 	return ret;
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837
 }
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838
 
839
+static struct inode *devmem_inode;
840
+
841
+#ifdef CONFIG_IO_STRICT_DEVMEM
842
+void revoke_devmem(struct resource *res)
843
+{
844
+	/* pairs with smp_store_release() in devmem_init_inode() */
845
+	struct inode *inode = smp_load_acquire(&devmem_inode);
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+
847
+	/*
848
+	 * Check that the initialization has completed. Losing the race
849
+	 * is ok because it means drivers are claiming resources before
850
+	 * the fs_initcall level of init and prevent /dev/mem from
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+	 * establishing mappings.
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+	 */
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+	if (!inode)
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+		return;
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+
856
+	/*
857
+	 * The expectation is that the driver has successfully marked
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+	 * the resource busy by this point, so devmem_is_allowed()
859
+	 * should start returning false, however for performance this
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+	 * does not iterate the entire resource range.
861
+	 */
862
+	if (devmem_is_allowed(PHYS_PFN(res->start)) &&
863
+	    devmem_is_allowed(PHYS_PFN(res->end))) {
864
+		/*
865
+		 * *cringe* iomem=relaxed says "go ahead, what's the
866
+		 * worst that can happen?"
867
+		 */
868
+		return;
869
+	}
870
+
871
+	unmap_mapping_range(inode->i_mapping, res->start, resource_size(res), 1);
872
+}
873
+#endif
874
+
808
875
 static int open_port(struct inode *inode, struct file *filp)
809
876
 {
810
-	return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
877
+	int rc;
878
+
879
+	if (!capable(CAP_SYS_RAWIO))
880
+		return -EPERM;
881
+
882
+	rc = security_locked_down(LOCKDOWN_DEV_MEM);
883
+	if (rc)
884
+		return rc;
885
+
886
+	if (iminor(inode) != DEVMEM_MINOR)
887
+		return 0;
888
+
889
+	/*
890
+	 * Use a unified address space to have a single point to manage
891
+	 * revocations when drivers want to take over a /dev/mem mapped
892
+	 * range.
893
+	 */
894
+	inode->i_mapping = devmem_inode->i_mapping;
895
+	filp->f_mapping = inode->i_mapping;
896
+
897
+	return 0;
811
898
 }
812
899
 
813
900
 #define zero_lseek	null_lseek
..
..
@@ -861,6 +948,7 @@
861
948
 	.llseek		= zero_lseek,
862
949
 	.write		= write_zero,
863
950
 	.read_iter	= read_iter_zero,
951
+	.read		= read_zero,
864
952
 	.write_iter	= write_iter_zero,
865
953
 	.mmap		= mmap_zero,
866
954
 	.get_unmapped_area = get_unmapped_area_zero,
..
..
@@ -882,7 +970,7 @@
882
970
 	fmode_t fmode;
883
971
 } devlist[] = {
884
972
 #ifdef CONFIG_DEVMEM
885
-	 [1] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET },
973
+	 [DEVMEM_MINOR] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET },
886
974
 #endif
887
975
 #ifdef CONFIG_DEVKMEM
888
976
 	 [2] = { "kmem", 0, &kmem_fops, FMODE_UNSIGNED_OFFSET },
..
..
@@ -893,8 +981,8 @@
893
981
 #endif
894
982
 	 [5] = { "zero", 0666, &zero_fops, 0 },
895
983
 	 [7] = { "full", 0666, &full_fops, 0 },
896
-	 [8] = { "random", 0666, &random_fops, 0 },
897
-	 [9] = { "urandom", 0666, &urandom_fops, 0 },
984
+	 [8] = { "random", 0666, &random_fops, FMODE_NOWAIT },
985
+	 [9] = { "urandom", 0666, &urandom_fops, FMODE_NOWAIT },
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986
 #ifdef CONFIG_PRINTK
899
987
 	[11] = { "kmsg", 0644, &kmsg_fops, 0 },
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 #endif
..
..
@@ -936,6 +1024,48 @@
936
1024
 
937
1025
 static struct class *mem_class;
938
1026
 
1027
+static int devmem_fs_init_fs_context(struct fs_context *fc)
1028
+{
1029
+	return init_pseudo(fc, DEVMEM_MAGIC) ? 0 : -ENOMEM;
1030
+}
1031
+
1032
+static struct file_system_type devmem_fs_type = {
1033
+	.name		= "devmem",
1034
+	.owner		= THIS_MODULE,
1035
+	.init_fs_context = devmem_fs_init_fs_context,
1036
+	.kill_sb	= kill_anon_super,
1037
+};
1038
+
1039
+static int devmem_init_inode(void)
1040
+{
1041
+	static struct vfsmount *devmem_vfs_mount;
1042
+	static int devmem_fs_cnt;
1043
+	struct inode *inode;
1044
+	int rc;
1045
+
1046
+	rc = simple_pin_fs(&devmem_fs_type, &devmem_vfs_mount, &devmem_fs_cnt);
1047
+	if (rc < 0) {
1048
+		pr_err("Cannot mount /dev/mem pseudo filesystem: %d\n", rc);
1049
+		return rc;
1050
+	}
1051
+
1052
+	inode = alloc_anon_inode(devmem_vfs_mount->mnt_sb);
1053
+	if (IS_ERR(inode)) {
1054
+		rc = PTR_ERR(inode);
1055
+		pr_err("Cannot allocate inode for /dev/mem: %d\n", rc);
1056
+		simple_release_fs(&devmem_vfs_mount, &devmem_fs_cnt);
1057
+		return rc;
1058
+	}
1059
+
1060
+	/*
1061
+	 * Publish /dev/mem initialized.
1062
+	 * Pairs with smp_load_acquire() in revoke_devmem().
1063
+	 */
1064
+	smp_store_release(&devmem_inode, inode);
1065
+
1066
+	return 0;
1067
+}
1068
+
939
1069
 static int __init chr_dev_init(void)
940
1070
 {
941
1071
 	int minor;
..
..
@@ -957,6 +1087,8 @@
957
1087
 		 */
958
1088
 		if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
959
1089
 			continue;
1090
+		if ((minor == DEVMEM_MINOR) && devmem_init_inode() != 0)
1091
+			continue;
960
1092
 
961
1093
 		device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
962
1094
 			      NULL, devlist[minor].name);