From: Dan Williams dan.j.williams@intel.com
[ Upstream commit 3234ac664a870e6ea69ae3a57d824cd7edbeacc5 ]
Close the hole of holding a mapping over kernel driver takeover event of a given address range.
Commit 90a545e98126 ("restrict /dev/mem to idle io memory ranges") introduced CONFIG_IO_STRICT_DEVMEM with the goal of protecting the kernel against scenarios where a /dev/mem user tramples memory that a kernel driver owns. However, this protection only prevents *new* read(), write() and mmap() requests. Established mappings prior to the driver calling request_mem_region() are left alone.
Especially with persistent memory, and the core kernel metadata that is stored there, there are plentiful scenarios for a /dev/mem user to violate the expectations of the driver and cause amplified damage.
Teach request_mem_region() to find and shoot down active /dev/mem mappings that it believes it has successfully claimed for the exclusive use of the driver. Effectively a driver call to request_mem_region() becomes a hole-punch on the /dev/mem device.
The typical usage of unmap_mapping_range() is part of truncate_pagecache() to punch a hole in a file, but in this case the implementation is only doing the "first half" of a hole punch. Namely it is just evacuating current established mappings of the "hole", and it relies on the fact that /dev/mem establishes mappings in terms of absolute physical address offsets. Once existing mmap users are invalidated they can attempt to re-establish the mapping, or attempt to continue issuing read(2) / write(2) to the invalidated extent, but they will then be subject to the CONFIG_IO_STRICT_DEVMEM checking that can block those subsequent accesses.
Cc: Arnd Bergmann arnd@arndb.de Cc: Ingo Molnar mingo@redhat.com Cc: Kees Cook keescook@chromium.org Cc: Matthew Wilcox willy@infradead.org Cc: Russell King linux@arm.linux.org.uk Cc: Andrew Morton akpm@linux-foundation.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Fixes: 90a545e98126 ("restrict /dev/mem to idle io memory ranges") Signed-off-by: Dan Williams dan.j.williams@intel.com Reviewed-by: Kees Cook keescook@chromium.org Link: https://lore.kernel.org/r/159009507306.847224.8502634072429766747.stgit@dwil... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/char/mem.c | 101 ++++++++++++++++++++++++++++++++++++- include/linux/ioport.h | 6 +++ include/uapi/linux/magic.h | 1 + kernel/resource.c | 5 ++ 4 files changed, 111 insertions(+), 2 deletions(-)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 43dd0891ca1e..31cae88a730b 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -31,11 +31,15 @@ #include <linux/uio.h> #include <linux/uaccess.h> #include <linux/security.h> +#include <linux/pseudo_fs.h> +#include <uapi/linux/magic.h> +#include <linux/mount.h>
#ifdef CONFIG_IA64 # include <linux/efi.h> #endif
+#define DEVMEM_MINOR 1 #define DEVPORT_MINOR 4
static inline unsigned long size_inside_page(unsigned long start, @@ -805,12 +809,64 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig) return ret; }
+static struct inode *devmem_inode; + +#ifdef CONFIG_IO_STRICT_DEVMEM +void revoke_devmem(struct resource *res) +{ + struct inode *inode = READ_ONCE(devmem_inode); + + /* + * Check that the initialization has completed. Losing the race + * is ok because it means drivers are claiming resources before + * the fs_initcall level of init and prevent /dev/mem from + * establishing mappings. + */ + if (!inode) + return; + + /* + * The expectation is that the driver has successfully marked + * the resource busy by this point, so devmem_is_allowed() + * should start returning false, however for performance this + * does not iterate the entire resource range. + */ + if (devmem_is_allowed(PHYS_PFN(res->start)) && + devmem_is_allowed(PHYS_PFN(res->end))) { + /* + * *cringe* iomem=relaxed says "go ahead, what's the + * worst that can happen?" + */ + return; + } + + unmap_mapping_range(inode->i_mapping, res->start, resource_size(res), 1); +} +#endif + static int open_port(struct inode *inode, struct file *filp) { + int rc; + if (!capable(CAP_SYS_RAWIO)) return -EPERM;
- return security_locked_down(LOCKDOWN_DEV_MEM); + rc = security_locked_down(LOCKDOWN_DEV_MEM); + if (rc) + return rc; + + if (iminor(inode) != DEVMEM_MINOR) + return 0; + + /* + * Use a unified address space to have a single point to manage + * revocations when drivers want to take over a /dev/mem mapped + * range. + */ + inode->i_mapping = devmem_inode->i_mapping; + filp->f_mapping = inode->i_mapping; + + return 0; }
#define zero_lseek null_lseek @@ -885,7 +941,7 @@ static const struct memdev { fmode_t fmode; } devlist[] = { #ifdef CONFIG_DEVMEM - [1] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET }, + [DEVMEM_MINOR] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET }, #endif #ifdef CONFIG_DEVKMEM [2] = { "kmem", 0, &kmem_fops, FMODE_UNSIGNED_OFFSET }, @@ -939,6 +995,45 @@ static char *mem_devnode(struct device *dev, umode_t *mode)
static struct class *mem_class;
+static int devmem_fs_init_fs_context(struct fs_context *fc) +{ + return init_pseudo(fc, DEVMEM_MAGIC) ? 0 : -ENOMEM; +} + +static struct file_system_type devmem_fs_type = { + .name = "devmem", + .owner = THIS_MODULE, + .init_fs_context = devmem_fs_init_fs_context, + .kill_sb = kill_anon_super, +}; + +static int devmem_init_inode(void) +{ + static struct vfsmount *devmem_vfs_mount; + static int devmem_fs_cnt; + struct inode *inode; + int rc; + + rc = simple_pin_fs(&devmem_fs_type, &devmem_vfs_mount, &devmem_fs_cnt); + if (rc < 0) { + pr_err("Cannot mount /dev/mem pseudo filesystem: %d\n", rc); + return rc; + } + + inode = alloc_anon_inode(devmem_vfs_mount->mnt_sb); + if (IS_ERR(inode)) { + rc = PTR_ERR(inode); + pr_err("Cannot allocate inode for /dev/mem: %d\n", rc); + simple_release_fs(&devmem_vfs_mount, &devmem_fs_cnt); + return rc; + } + + /* publish /dev/mem initialized */ + WRITE_ONCE(devmem_inode, inode); + + return 0; +} + static int __init chr_dev_init(void) { int minor; @@ -960,6 +1055,8 @@ static int __init chr_dev_init(void) */ if ((minor == DEVPORT_MINOR) && !arch_has_dev_port()) continue; + if ((minor == DEVMEM_MINOR) && devmem_init_inode() != 0) + continue;
device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor), NULL, devlist[minor].name); diff --git a/include/linux/ioport.h b/include/linux/ioport.h index 7bddddfc76d6..fdc201d61460 100644 --- a/include/linux/ioport.h +++ b/include/linux/ioport.h @@ -300,5 +300,11 @@ struct resource *devm_request_free_mem_region(struct device *dev, struct resource *request_free_mem_region(struct resource *base, unsigned long size, const char *name);
+#ifdef CONFIG_IO_STRICT_DEVMEM +void revoke_devmem(struct resource *res); +#else +static inline void revoke_devmem(struct resource *res) { }; +#endif + #endif /* __ASSEMBLY__ */ #endif /* _LINUX_IOPORT_H */ diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h index 903cc2d2750b..84ae605c0643 100644 --- a/include/uapi/linux/magic.h +++ b/include/uapi/linux/magic.h @@ -93,6 +93,7 @@ #define BALLOON_KVM_MAGIC 0x13661366 #define ZSMALLOC_MAGIC 0x58295829 #define DMA_BUF_MAGIC 0x444d4142 /* "DMAB" */ +#define DEVMEM_MAGIC 0x454d444d /* "DMEM" */ #define Z3FOLD_MAGIC 0x33
#endif /* __LINUX_MAGIC_H__ */ diff --git a/kernel/resource.c b/kernel/resource.c index 76036a41143b..841737bbda9e 100644 --- a/kernel/resource.c +++ b/kernel/resource.c @@ -1126,6 +1126,7 @@ struct resource * __request_region(struct resource *parent, { DECLARE_WAITQUEUE(wait, current); struct resource *res = alloc_resource(GFP_KERNEL); + struct resource *orig_parent = parent;
if (!res) return NULL; @@ -1176,6 +1177,10 @@ struct resource * __request_region(struct resource *parent, break; } write_unlock(&resource_lock); + + if (res && orig_parent == &iomem_resource) + revoke_devmem(res); + return res; } EXPORT_SYMBOL(__request_region);