Message ID | 20171024152415.22864-2-jack@suse.cz |
---|---|
State | Superseded, archived |
Headers | show |
Series | dax, ext4, xfs: Synchronous page faults | expand |
On Tue, Oct 24, 2017 at 05:23:58PM +0200, Jan Kara wrote: > From: Dan Williams <dan.j.williams@intel.com> > > The mmap(2) syscall suffers from the ABI anti-pattern of not validating > unknown flags. However, proposals like MAP_SYNC need a mechanism to > define new behavior that is known to fail on older kernels without the > support. Define a new MAP_SHARED_VALIDATE flag pattern that is > guaranteed to fail on all legacy mmap implementations. > > It is worth noting that the original proposal was for a standalone > MAP_VALIDATE flag. However, when that could not be supported by all > archs Linus observed: > > I see why you *think* you want a bitmap. You think you want > a bitmap because you want to make MAP_VALIDATE be part of MAP_SYNC > etc, so that people can do > > ret = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED > | MAP_SYNC, fd, 0); > > and "know" that MAP_SYNC actually takes. > > And I'm saying that whole wish is bogus. You're fundamentally > depending on special semantics, just make it explicit. It's already > not portable, so don't try to make it so. > > Rename that MAP_VALIDATE as MAP_SHARED_VALIDATE, make it have a value > of 0x3, and make people do > > ret = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED_VALIDATE > | MAP_SYNC, fd, 0); > > and then the kernel side is easier too (none of that random garbage > playing games with looking at the "MAP_VALIDATE bit", but just another > case statement in that map type thing. > > Boom. Done. > > Similar to ->fallocate() we also want the ability to validate the > support for new flags on a per ->mmap() 'struct file_operations' > instance basis. Towards that end arrange for flags to be generically > validated against a mmap_supported_flags exported by 'struct > file_operations'. By default all existing flags are implicitly > supported, but new flags require MAP_SHARED_VALIDATE and > per-instance-opt-in. > > Cc: Jan Kara <jack@suse.cz> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Andy Lutomirski <luto@kernel.org> > Cc: Andrew Morton <akpm@linux-foundation.org> > Suggested-by: Christoph Hellwig <hch@lst.de> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> > Signed-off-by: Dan Williams <dan.j.williams@intel.com> > Signed-off-by: Jan Kara <jack@suse.cz> Looks great. Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h index 3b26cc62dadb..f6d118aaedb9 100644 --- a/arch/alpha/include/uapi/asm/mman.h +++ b/arch/alpha/include/uapi/asm/mman.h @@ -11,6 +11,7 @@ #define MAP_SHARED 0x01 /* Share changes */ #define MAP_PRIVATE 0x02 /* Changes are private */ +#define MAP_SHARED_VALIDATE 0x03 /* share + validate extension flags */ #define MAP_TYPE 0x0f /* Mask for type of mapping (OSF/1 is _wrong_) */ #define MAP_FIXED 0x100 /* Interpret addr exactly */ #define MAP_ANONYMOUS 0x10 /* don't use a file */ diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h index da3216007fe0..93268e4cd3c7 100644 --- a/arch/mips/include/uapi/asm/mman.h +++ b/arch/mips/include/uapi/asm/mman.h @@ -28,6 +28,7 @@ */ #define MAP_SHARED 0x001 /* Share changes */ #define MAP_PRIVATE 0x002 /* Changes are private */ +#define MAP_SHARED_VALIDATE 0x003 /* share + validate extension flags */ #define MAP_TYPE 0x00f /* Mask for type of mapping */ #define MAP_FIXED 0x010 /* Interpret addr exactly */ diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h index 775b5d5e41a1..bca652aa1677 100644 --- a/arch/parisc/include/uapi/asm/mman.h +++ b/arch/parisc/include/uapi/asm/mman.h @@ -11,6 +11,7 @@ #define MAP_SHARED 0x01 /* Share changes */ #define MAP_PRIVATE 0x02 /* Changes are private */ +#define MAP_SHARED_VALIDATE 0x03 /* share + validate extension flags */ #define MAP_TYPE 0x03 /* Mask for type of mapping */ #define MAP_FIXED 0x04 /* Interpret addr exactly */ #define MAP_ANONYMOUS 0x10 /* don't use a file */ diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h index b15b278aa314..9ab426374714 100644 --- a/arch/xtensa/include/uapi/asm/mman.h +++ b/arch/xtensa/include/uapi/asm/mman.h @@ -35,6 +35,7 @@ */ #define MAP_SHARED 0x001 /* Share changes */ #define MAP_PRIVATE 0x002 /* Changes are private */ +#define MAP_SHARED_VALIDATE 0x003 /* share + validate extension flags */ #define MAP_TYPE 0x00f /* Mask for type of mapping */ #define MAP_FIXED 0x010 /* Interpret addr exactly */ diff --git a/include/linux/fs.h b/include/linux/fs.h index 13dab191a23e..57added3201d 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1701,6 +1701,7 @@ struct file_operations { long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long); long (*compat_ioctl) (struct file *, unsigned int, unsigned long); int (*mmap) (struct file *, struct vm_area_struct *); + unsigned long mmap_supported_flags; int (*open) (struct inode *, struct file *); int (*flush) (struct file *, fl_owner_t id); int (*release) (struct inode *, struct file *); diff --git a/include/linux/mman.h b/include/linux/mman.h index c8367041fafd..94b63b4d71ff 100644 --- a/include/linux/mman.h +++ b/include/linux/mman.h @@ -7,6 +7,45 @@ #include <linux/atomic.h> #include <uapi/linux/mman.h> +/* + * Arrange for legacy / undefined architecture specific flags to be + * ignored by default in LEGACY_MAP_MASK. + */ +#ifndef MAP_32BIT +#define MAP_32BIT 0 +#endif +#ifndef MAP_HUGE_2MB +#define MAP_HUGE_2MB 0 +#endif +#ifndef MAP_HUGE_1GB +#define MAP_HUGE_1GB 0 +#endif +#ifndef MAP_UNINITIALIZED +#define MAP_UNINITIALIZED 0 +#endif + +/* + * The historical set of flags that all mmap implementations implicitly + * support when a ->mmap_validate() op is not provided in file_operations. + */ +#define LEGACY_MAP_MASK (MAP_SHARED \ + | MAP_PRIVATE \ + | MAP_FIXED \ + | MAP_ANONYMOUS \ + | MAP_DENYWRITE \ + | MAP_EXECUTABLE \ + | MAP_UNINITIALIZED \ + | MAP_GROWSDOWN \ + | MAP_LOCKED \ + | MAP_NORESERVE \ + | MAP_POPULATE \ + | MAP_NONBLOCK \ + | MAP_STACK \ + | MAP_HUGETLB \ + | MAP_32BIT \ + | MAP_HUGE_2MB \ + | MAP_HUGE_1GB) + extern int sysctl_overcommit_memory; extern int sysctl_overcommit_ratio; extern unsigned long sysctl_overcommit_kbytes; diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h index 203268f9231e..8ce7f5a0800f 100644 --- a/include/uapi/asm-generic/mman-common.h +++ b/include/uapi/asm-generic/mman-common.h @@ -16,6 +16,7 @@ #define MAP_SHARED 0x01 /* Share changes */ #define MAP_PRIVATE 0x02 /* Changes are private */ +#define MAP_SHARED_VALIDATE 0x03 /* share + validate extension flags */ #define MAP_TYPE 0x0f /* Mask for type of mapping */ #define MAP_FIXED 0x10 /* Interpret addr exactly */ #define MAP_ANONYMOUS 0x20 /* don't use a file */ diff --git a/mm/mmap.c b/mm/mmap.c index 680506faceae..924839fac0e6 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1387,9 +1387,24 @@ unsigned long do_mmap(struct file *file, unsigned long addr, if (file) { struct inode *inode = file_inode(file); + unsigned long flags_mask; + + flags_mask = LEGACY_MAP_MASK | file->f_op->mmap_supported_flags; switch (flags & MAP_TYPE) { case MAP_SHARED: + /* + * Force use of MAP_SHARED_VALIDATE with non-legacy + * flags. E.g. MAP_SYNC is dangerous to use with + * MAP_SHARED as you don't know which consistency model + * you will get. We silently ignore unsupported flags + * with MAP_SHARED to preserve backward compatibility. + */ + flags &= LEGACY_MAP_MASK; + /* fall through */ + case MAP_SHARED_VALIDATE: + if (flags & ~flags_mask) + return -EOPNOTSUPP; if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE)) return -EACCES; diff --git a/tools/include/uapi/asm-generic/mman-common.h b/tools/include/uapi/asm-generic/mman-common.h index 203268f9231e..8ce7f5a0800f 100644 --- a/tools/include/uapi/asm-generic/mman-common.h +++ b/tools/include/uapi/asm-generic/mman-common.h @@ -16,6 +16,7 @@ #define MAP_SHARED 0x01 /* Share changes */ #define MAP_PRIVATE 0x02 /* Changes are private */ +#define MAP_SHARED_VALIDATE 0x03 /* share + validate extension flags */ #define MAP_TYPE 0x0f /* Mask for type of mapping */ #define MAP_FIXED 0x10 /* Interpret addr exactly */ #define MAP_ANONYMOUS 0x20 /* don't use a file */