| Message ID | 150764694114.16882.5128952296874418457.stgit@dwillia2-desk3.amr.corp.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue 10-10-17 07:49:01, Dan Williams wrote: > The mmap(2) syscall suffers from the ABI anti-pattern of not validating > unknown flags. However, proposals like MAP_SYNC and MAP_DIRECT 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_mask 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> > --- > arch/alpha/include/uapi/asm/mman.h | 1 + > arch/mips/include/uapi/asm/mman.h | 1 + > arch/mips/kernel/vdso.c | 2 + > arch/parisc/include/uapi/asm/mman.h | 1 + > arch/tile/mm/elf.c | 3 +- > arch/xtensa/include/uapi/asm/mman.h | 1 + > include/linux/fs.h | 2 + > include/linux/mm.h | 2 + > include/linux/mman.h | 39 ++++++++++++++++++++++++++ > include/uapi/asm-generic/mman-common.h | 1 + > mm/mmap.c | 21 ++++++++++++-- > tools/include/uapi/asm-generic/mman-common.h | 1 + > 12 files changed, 69 insertions(+), 6 deletions(-) > > diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h > index 3b26cc62dadb..92823f24890b 100644 > --- a/arch/alpha/include/uapi/asm/mman.h > +++ b/arch/alpha/include/uapi/asm/mman.h > @@ -14,6 +14,7 @@ > #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 */ > +#define MAP_SHARED_VALIDATE 0x3 /* share + validate extension flags */ Just a nit but I'd put definition of MAP_SHARED_VALIDATE close to the definition of MAP_SHARED and MAP_PRIVATE where it logically belongs (for all archs). > diff --git a/include/linux/mm.h b/include/linux/mm.h > index f8c10d336e42..5c4c98e4adc9 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2133,7 +2133,7 @@ extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned lo > > extern unsigned long mmap_region(struct file *file, unsigned long addr, > unsigned long len, vm_flags_t vm_flags, unsigned long pgoff, > - struct list_head *uf); > + struct list_head *uf, unsigned long map_flags); > extern unsigned long do_mmap(struct file *file, unsigned long addr, > unsigned long len, unsigned long prot, unsigned long flags, > vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate, I have to say I'm not very keen on passing down both vm_flags and map_flags - vm_flags are almost a subset of map_flags but not quite and the ambiguity which needs to be used for a particular check seems to open a space for errors. Granted you currently only care about MAP_DIRECT in ->mmap_validate and just pass map_flags through mmap_region() so there's no space for confusion but future checks could do something different. But OTOH I don't see a cleaner way of avoiding the need to allocate vma flag for something you need to check down in ->mmap_validate so I guess I'll live with that and if problems really happen, we may have cleaner idea what needs to be done. So overall feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza
On Wed, Oct 11, 2017 at 12:43 AM, Jan Kara <jack@suse.cz> wrote: > On Tue 10-10-17 07:49:01, Dan Williams wrote: >> The mmap(2) syscall suffers from the ABI anti-pattern of not validating >> unknown flags. However, proposals like MAP_SYNC and MAP_DIRECT 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_mask 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> >> --- >> arch/alpha/include/uapi/asm/mman.h | 1 + >> arch/mips/include/uapi/asm/mman.h | 1 + >> arch/mips/kernel/vdso.c | 2 + >> arch/parisc/include/uapi/asm/mman.h | 1 + >> arch/tile/mm/elf.c | 3 +- >> arch/xtensa/include/uapi/asm/mman.h | 1 + >> include/linux/fs.h | 2 + >> include/linux/mm.h | 2 + >> include/linux/mman.h | 39 ++++++++++++++++++++++++++ >> include/uapi/asm-generic/mman-common.h | 1 + >> mm/mmap.c | 21 ++++++++++++-- >> tools/include/uapi/asm-generic/mman-common.h | 1 + >> 12 files changed, 69 insertions(+), 6 deletions(-) >> >> diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h >> index 3b26cc62dadb..92823f24890b 100644 >> --- a/arch/alpha/include/uapi/asm/mman.h >> +++ b/arch/alpha/include/uapi/asm/mman.h >> @@ -14,6 +14,7 @@ >> #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 */ >> +#define MAP_SHARED_VALIDATE 0x3 /* share + validate extension flags */ > > Just a nit but I'd put definition of MAP_SHARED_VALIDATE close to the > definition of MAP_SHARED and MAP_PRIVATE where it logically belongs (for > all archs). Will do. > >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index f8c10d336e42..5c4c98e4adc9 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -2133,7 +2133,7 @@ extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned lo >> >> extern unsigned long mmap_region(struct file *file, unsigned long addr, >> unsigned long len, vm_flags_t vm_flags, unsigned long pgoff, >> - struct list_head *uf); >> + struct list_head *uf, unsigned long map_flags); >> extern unsigned long do_mmap(struct file *file, unsigned long addr, >> unsigned long len, unsigned long prot, unsigned long flags, >> vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate, > > I have to say I'm not very keen on passing down both vm_flags and map_flags > - vm_flags are almost a subset of map_flags but not quite and the ambiguity > which needs to be used for a particular check seems to open a space for > errors. Granted you currently only care about MAP_DIRECT in ->mmap_validate > and just pass map_flags through mmap_region() so there's no space for > confusion but future checks could do something different. I was hoping the fact that one can't trigger a call to ->mmap_validate() unless they specify a flag outside of LEGACY_MAP_MASK makes it clearer that validation is only for new flags. Old flags get the existing "may be silently ignored" behavior. > But OTOH I don't > see a cleaner way of avoiding the need to allocate vma flag for something > you need to check down in ->mmap_validate so I guess I'll live with that > and if problems really happen, we may have cleaner idea what needs to be > done. > > So overall feel free to add: > > Reviewed-by: Jan Kara <jack@suse.cz> Thanks Jan.
diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h index 3b26cc62dadb..92823f24890b 100644 --- a/arch/alpha/include/uapi/asm/mman.h +++ b/arch/alpha/include/uapi/asm/mman.h @@ -14,6 +14,7 @@ #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 */ +#define MAP_SHARED_VALIDATE 0x3 /* share + validate extension flags */ /* not used by linux, but here to make sure we don't clash with OSF/1 defines */ #define _MAP_HASSEMAPHORE 0x0200 diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h index da3216007fe0..c77689076577 100644 --- a/arch/mips/include/uapi/asm/mman.h +++ b/arch/mips/include/uapi/asm/mman.h @@ -30,6 +30,7 @@ #define MAP_PRIVATE 0x002 /* Changes are private */ #define MAP_TYPE 0x00f /* Mask for type of mapping */ #define MAP_FIXED 0x010 /* Interpret addr exactly */ +#define MAP_SHARED_VALIDATE 0x3 /* share + validate extension flags */ /* not used by linux, but here to make sure we don't clash with ABI defines */ #define MAP_RENAME 0x020 /* Assign page to file */ diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c index 019035d7225c..cf10654477a9 100644 --- a/arch/mips/kernel/vdso.c +++ b/arch/mips/kernel/vdso.c @@ -110,7 +110,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp) base = mmap_region(NULL, STACK_TOP, PAGE_SIZE, VM_READ|VM_WRITE|VM_EXEC| VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, - 0, NULL); + 0, NULL, 0); if (IS_ERR_VALUE(base)) { ret = base; goto out; diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h index 775b5d5e41a1..36b688d52de3 100644 --- a/arch/parisc/include/uapi/asm/mman.h +++ b/arch/parisc/include/uapi/asm/mman.h @@ -14,6 +14,7 @@ #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 */ +#define MAP_SHARED_VALIDATE 0x3 /* share + validate extension flags */ #define MAP_DENYWRITE 0x0800 /* ETXTBSY */ #define MAP_EXECUTABLE 0x1000 /* mark it as an executable */ diff --git a/arch/tile/mm/elf.c b/arch/tile/mm/elf.c index 889901824400..5ffcbe76aef9 100644 --- a/arch/tile/mm/elf.c +++ b/arch/tile/mm/elf.c @@ -143,7 +143,8 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, unsigned long addr = MEM_USER_INTRPT; addr = mmap_region(NULL, addr, INTRPT_SIZE, VM_READ|VM_EXEC| - VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, 0, NULL); + VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, 0, + NULL, 0); if (addr > (unsigned long) -PAGE_SIZE) retval = (int) addr; } diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h index b15b278aa314..ec597900eec7 100644 --- a/arch/xtensa/include/uapi/asm/mman.h +++ b/arch/xtensa/include/uapi/asm/mman.h @@ -37,6 +37,7 @@ #define MAP_PRIVATE 0x002 /* Changes are private */ #define MAP_TYPE 0x00f /* Mask for type of mapping */ #define MAP_FIXED 0x010 /* Interpret addr exactly */ +#define MAP_SHARED_VALIDATE 0x3 /* share + validate extension flags */ /* not used by linux, but here to make sure we don't clash with ABI defines */ #define MAP_RENAME 0x020 /* Assign page to file */ diff --git a/include/linux/fs.h b/include/linux/fs.h index 339e73742e73..51538958f7f5 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1701,6 +1701,8 @@ 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 *); + int (*mmap_validate) (struct file *, struct vm_area_struct *, + unsigned long); 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/mm.h b/include/linux/mm.h index f8c10d336e42..5c4c98e4adc9 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2133,7 +2133,7 @@ extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned lo extern unsigned long mmap_region(struct file *file, unsigned long addr, unsigned long len, vm_flags_t vm_flags, unsigned long pgoff, - struct list_head *uf); + struct list_head *uf, unsigned long map_flags); extern unsigned long do_mmap(struct file *file, unsigned long addr, unsigned long len, unsigned long prot, unsigned long flags, vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate, 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..ac55d1c0ec0f 100644 --- a/include/uapi/asm-generic/mman-common.h +++ b/include/uapi/asm-generic/mman-common.h @@ -24,6 +24,7 @@ #else # define MAP_UNINITIALIZED 0x0 /* Don't support this flag */ #endif +#define MAP_SHARED_VALIDATE 0x3 /* share + validate extension flags */ /* * Flags for mlock diff --git a/mm/mmap.c b/mm/mmap.c index 680506faceae..a1bcaa9eff42 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1389,6 +1389,18 @@ unsigned long do_mmap(struct file *file, unsigned long addr, struct inode *inode = file_inode(file); switch (flags & MAP_TYPE) { + case (MAP_SHARED_VALIDATE): + if ((flags & ~LEGACY_MAP_MASK) == 0) { + /* + * If all legacy mmap flags, downgrade + * to MAP_SHARED, i.e. invoke ->mmap() + * instead of ->mmap_validate() + */ + flags &= ~MAP_TYPE; + flags |= MAP_SHARED; + } else if (!file->f_op->mmap_validate) + return -EOPNOTSUPP; + /* fall through */ case MAP_SHARED: if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE)) return -EACCES; @@ -1465,7 +1477,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr, vm_flags |= VM_NORESERVE; } - addr = mmap_region(file, addr, len, vm_flags, pgoff, uf); + addr = mmap_region(file, addr, len, vm_flags, pgoff, uf, flags); if (!IS_ERR_VALUE(addr) && ((vm_flags & VM_LOCKED) || (flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE)) @@ -1602,7 +1614,7 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags) unsigned long mmap_region(struct file *file, unsigned long addr, unsigned long len, vm_flags_t vm_flags, unsigned long pgoff, - struct list_head *uf) + struct list_head *uf, unsigned long map_flags) { struct mm_struct *mm = current->mm; struct vm_area_struct *vma, *prev; @@ -1687,7 +1699,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr, * new file must not have been exposed to user-space, yet. */ vma->vm_file = get_file(file); - error = call_mmap(file, vma); + if ((map_flags & MAP_TYPE) == MAP_SHARED_VALIDATE) + error = file->f_op->mmap_validate(file, vma, map_flags); + else + error = call_mmap(file, vma); if (error) goto unmap_and_free_vma; diff --git a/tools/include/uapi/asm-generic/mman-common.h b/tools/include/uapi/asm-generic/mman-common.h index 8c27db0c5c08..202bc4277fb5 100644 --- a/tools/include/uapi/asm-generic/mman-common.h +++ b/tools/include/uapi/asm-generic/mman-common.h @@ -24,6 +24,7 @@ #else # define MAP_UNINITIALIZED 0x0 /* Don't support this flag */ #endif +#define MAP_SHARED_VALIDATE 0x3 /* share + validate extension flags */ /* * Flags for mlock
The mmap(2) syscall suffers from the ABI anti-pattern of not validating unknown flags. However, proposals like MAP_SYNC and MAP_DIRECT 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_mask 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> --- arch/alpha/include/uapi/asm/mman.h | 1 + arch/mips/include/uapi/asm/mman.h | 1 + arch/mips/kernel/vdso.c | 2 + arch/parisc/include/uapi/asm/mman.h | 1 + arch/tile/mm/elf.c | 3 +- arch/xtensa/include/uapi/asm/mman.h | 1 + include/linux/fs.h | 2 + include/linux/mm.h | 2 + include/linux/mman.h | 39 ++++++++++++++++++++++++++ include/uapi/asm-generic/mman-common.h | 1 + mm/mmap.c | 21 ++++++++++++-- tools/include/uapi/asm-generic/mman-common.h | 1 + 12 files changed, 69 insertions(+), 6 deletions(-)