Re: [PATCH RFC v3 27/36] kmsan: hooks for copy_to_user() and friends

[Andrey Konovalov <andreyknvl@google.com>]

On Thu, Dec 5, 2019 at 5:00 PM Alexander Potapenko <glider@google.com> wrote:
>
> On Fri, Nov 29, 2019 at 4:34 PM Andrey Konovalov <andreyknvl@google.com> wrote:
> >
> > On Fri, Nov 22, 2019 at 12:27 PM <glider@google.com> wrote:
> > >
> > > Memory that is copied from userspace must be unpoisoned.
> > > Before copying memory to userspace, check it and report an error if it
> > > contains uninitialized bits.
> > >
> > > Signed-off-by: Alexander Potapenko <glider@google.com>
> > > To: Alexander Potapenko <glider@google.com>
> > > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > > Cc: Vegard Nossum <vegard.nossum@oracle.com>
> > > Cc: Dmitry Vyukov <dvyukov@google.com>
> > > Cc: linux-mm@kvack.org
> > > ---
> > > v3:
> > >  - fixed compilation errors reported by kbuild test bot
> > >
> > > Change-Id: I38428b9c7d1909b8441dcec1749b080494a7af99
> > > ---
> > >  arch/x86/include/asm/uaccess.h   | 12 ++++++++++++
> > >  include/asm-generic/cacheflush.h |  7 ++++++-
> > >  include/asm-generic/uaccess.h    | 12 ++++++++++--
> > >  include/linux/uaccess.h          | 32 +++++++++++++++++++++++++++-----
> > >  lib/iov_iter.c                   |  6 ++++++
> > >  lib/usercopy.c                   |  6 +++++-
> > >  6 files changed, 66 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> > > index 61d93f062a36..ac4b26583f7c 100644
> > > --- a/arch/x86/include/asm/uaccess.h
> > > +++ b/arch/x86/include/asm/uaccess.h
> > > @@ -6,6 +6,7 @@
> > >   */
> > >  #include <linux/compiler.h>
> > >  #include <linux/kasan-checks.h>
> > > +#include <linux/kmsan-checks.h>
> > >  #include <linux/string.h>
> > >  #include <asm/asm.h>
> > >  #include <asm/page.h>
> > > @@ -174,6 +175,7 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
> > >                         ASM_CALL_CONSTRAINT                             \
> > >                      : "0" (ptr), "i" (sizeof(*(ptr))));                \
> > >         (x) = (__force __typeof__(*(ptr))) __val_gu;                    \
> > > +       kmsan_unpoison_shadow(&(x), sizeof(*(ptr)));                    \
> > >         __builtin_expect(__ret_gu, 0);                                  \
> > >  })
> > >
> > > @@ -248,6 +250,7 @@ extern void __put_user_8(void);
> > >         __chk_user_ptr(ptr);                                    \
> > >         might_fault();                                          \
> > >         __pu_val = x;                                           \
> > > +       kmsan_check_memory(&(__pu_val), sizeof(*(ptr)));        \
> > >         switch (sizeof(*(ptr))) {                               \
> > >         case 1:                                                 \
> > >                 __put_user_x(1, __pu_val, ptr, __ret_pu);       \
> > > @@ -270,7 +273,9 @@ extern void __put_user_8(void);
> > >
> > >  #define __put_user_size(x, ptr, size, label)                           \
> > >  do {                                                                   \
> > > +       __typeof__(*(ptr)) __pus_val = x;                               \
> > >         __chk_user_ptr(ptr);                                            \
> > > +       kmsan_check_memory(&(__pus_val), size);                         \
> > >         switch (size) {                                                 \
> > >         case 1:                                                         \
> > >                 __put_user_goto(x, ptr, "b", "b", "iq", label); \
> > > @@ -295,7 +300,10 @@ do {                                                                       \
> > >   */
> > >  #define __put_user_size_ex(x, ptr, size)                               \
> > >  do {                                                                   \
> > > +       __typeof__(*(ptr)) __puse_val;                                  \
> >
> > Can we do = x here?
> Yes. Fixed, thanks!
> > >         __chk_user_ptr(ptr);                                            \
> > > +       __puse_val = x;                                                 \
> > > +       kmsan_check_memory(&(__puse_val), size);                        \
> > >         switch (size) {                                                 \
> > >         case 1:                                                         \
> > >                 __put_user_asm_ex(x, ptr, "b", "b", "iq");              \
> > > @@ -363,6 +371,7 @@ do {                                                                        \
> > >         default:                                                        \
> > >                 (x) = __get_user_bad();                                 \
> > >         }                                                               \
> > > +       kmsan_unpoison_shadow(&(x), size);                              \
> > >  } while (0)
> > >
> > >  #define __get_user_asm(x, addr, err, itype, rtype, ltype, errret)      \
> > > @@ -413,6 +422,7 @@ do {                                                                        \
> > >         default:                                                        \
> > >                 (x) = __get_user_bad();                                 \
> > >         }                                                               \
> > > +       kmsan_unpoison_shadow(&(x), size);                              \
> > >  } while (0)
> > >
> > >  #define __get_user_asm_ex(x, addr, itype, rtype, ltype)                        \
> > > @@ -428,11 +438,13 @@ do {                                                                      \
> > >  #define __put_user_nocheck(x, ptr, size)                       \
> > >  ({                                                             \
> > >         __label__ __pu_label;                                   \
> > > +       __typeof__(*(ptr)) __pun_val = x;                       \
> >
> > Not sure if this matters, but two lines below do (x).
> Right.
> > Also, why can't we use __pu_val instead of defining __pun_val?
> Will do.
> >
> > >         int __pu_err = -EFAULT;                                 \
> > >         __typeof__(*(ptr)) __pu_val = (x);                      \
> > >         __typeof__(ptr) __pu_ptr = (ptr);                       \
> > >         __typeof__(size) __pu_size = (size);                    \
> > >         __uaccess_begin();                                      \
> > > +       kmsan_check_memory(&(__pun_val), size);                 \
> > >         __put_user_size(__pu_val, __pu_ptr, __pu_size, __pu_label);     \
> > >         __pu_err = 0;                                           \
> > >  __pu_label:                                                    \
> > > diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h
> > > index a950a22c4890..707531dccf5e 100644
> > > --- a/include/asm-generic/cacheflush.h
> > > +++ b/include/asm-generic/cacheflush.h
> > > @@ -4,6 +4,7 @@
> > >
> > >  /* Keep includes the same across arches.  */
> > >  #include <linux/mm.h>
> > > +#include <linux/kmsan-checks.h>
> > >
> > >  #define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 0
> > >
> > > @@ -72,10 +73,14 @@ static inline void flush_cache_vunmap(unsigned long start, unsigned long end)
> > >
> > >  #define copy_to_user_page(vma, page, vaddr, dst, src, len) \
> > >         do { \
> > > +               kmsan_check_memory(src, len); \
> > >                 memcpy(dst, src, len); \
> > >                 flush_icache_user_range(vma, page, vaddr, len); \
> > >         } while (0)
> > >  #define copy_from_user_page(vma, page, vaddr, dst, src, len) \
> > > -       memcpy(dst, src, len)
> > > +       do { \
> > > +               memcpy(dst, src, len); \
> > > +               kmsan_unpoison_shadow(dst, len); \
> > > +       } while (0)
> > >
> > >  #endif /* __ASM_CACHEFLUSH_H */
> > > diff --git a/include/asm-generic/uaccess.h b/include/asm-generic/uaccess.h
> > > index e935318804f8..508ee649aeef 100644
> > > --- a/include/asm-generic/uaccess.h
> > > +++ b/include/asm-generic/uaccess.h
> > > @@ -142,7 +142,11 @@ static inline int __access_ok(unsigned long addr, unsigned long size)
> > >
> > >  static inline int __put_user_fn(size_t size, void __user *ptr, void *x)
> > >  {
> > > -       return unlikely(raw_copy_to_user(ptr, x, size)) ? -EFAULT : 0;
> > > +       int n;
> > > +
> > > +       n = raw_copy_to_user(ptr, x, size);
> > > +       kmsan_copy_to_user(ptr, x, size, n);
> > > +       return unlikely(n) ? -EFAULT : 0;
> > >  }
> > >
> > >  #define __put_user_fn(sz, u, k)        __put_user_fn(sz, u, k)
> > > @@ -203,7 +207,11 @@ extern int __put_user_bad(void) __attribute__((noreturn));
> > >  #ifndef __get_user_fn
> > >  static inline int __get_user_fn(size_t size, const void __user *ptr, void *x)
> > >  {
> > > -       return unlikely(raw_copy_from_user(x, ptr, size)) ? -EFAULT : 0;
> > > +       int copied, to_copy = size;
> > > +
> > > +       copied = raw_copy_from_user(x, ptr, size);
> > > +       kmsan_unpoison_shadow(x, to_copy - copied);
> > > +       return unlikely(copied) ? -EFAULT : 0;
> > >  }
> > >
> > >  #define __get_user_fn(sz, u, k)        __get_user_fn(sz, u, k)
> > > diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> > > index d4ee6e942562..7550d11a8077 100644
> > > --- a/include/linux/uaccess.h
> > > +++ b/include/linux/uaccess.h
> > > @@ -5,6 +5,7 @@
> > >  #include <linux/sched.h>
> > >  #include <linux/thread_info.h>
> > >  #include <linux/kasan-checks.h>
> > > +#include <linux/kmsan-checks.h>
> > >
> > >  #define uaccess_kernel() segment_eq(get_fs(), KERNEL_DS)
> > >
> > > @@ -58,18 +59,26 @@
> > >  static __always_inline __must_check unsigned long
> > >  __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
> > >  {
> > > +       unsigned long to_copy = n;
> > > +
> > >         kasan_check_write(to, n);
> > >         check_object_size(to, n, false);
> > > -       return raw_copy_from_user(to, from, n);
> > > +       n = raw_copy_from_user(to, from, n);
> > > +       kmsan_unpoison_shadow(to, to_copy - n);
> > > +       return n;
> > >  }
> > >
> > >  static __always_inline __must_check unsigned long
> > >  __copy_from_user(void *to, const void __user *from, unsigned long n)
> > >  {
> > > +       unsigned long to_copy = n;
> >
> > This is confusing. I think we need a var for raw_copy_from_user()
> > return value instead. Same in functions above and below.
> raw_copy_from_user() returns the number of bytes _not_ copied from
> userspace. So in the case it returns 0 we need to unpoison to_copy
> bytes.

My point was that reasiggning the value of n to the return value of
raw_copy_from_user(), but saving the original n into to_copy is
confusing. It would be easier to read this code, is n was left as is,
and there was a new var for raw_copy_from_user() return value.

> > > +
> > >         might_fault();
> > >         kasan_check_write(to, n);
> > >         check_object_size(to, n, false);
> > > -       return raw_copy_from_user(to, from, n);
> > > +       n = raw_copy_from_user(to, from, n);
> > > +       kmsan_unpoison_shadow(to, to_copy - n);
> > > +       return n;
> > >  }
> > >
> > >  /**
> > > @@ -88,29 +97,39 @@ __copy_from_user(void *to, const void __user *from, unsigned long n)
> > >  static __always_inline __must_check unsigned long
> > >  __copy_to_user_inatomic(void __user *to, const void *from, unsigned long n)
> > >  {
> > > +       unsigned long to_copy = n;
> > > +
> > >         kasan_check_read(from, n);
> > >         check_object_size(from, n, true);
> > > -       return raw_copy_to_user(to, from, n);
> > > +       n = raw_copy_to_user(to, from, n);
> > > +       kmsan_copy_to_user((const void *)to, from, to_copy, n);
> > > +       return n;
> > >  }
> > >
> > >  static __always_inline __must_check unsigned long
> > >  __copy_to_user(void __user *to, const void *from, unsigned long n)
> > >  {
> > > +       unsigned long to_copy = n;
> > > +
> > >         might_fault();
> > >         kasan_check_read(from, n);
> > >         check_object_size(from, n, true);
> > > -       return raw_copy_to_user(to, from, n);
> > > +       n = raw_copy_to_user(to, from, n);
> > > +       kmsan_copy_to_user((const void *)to, from, to_copy, n);
> > > +       return n;
> > >  }
> > >
> > >  #ifdef INLINE_COPY_FROM_USER
> > >  static inline __must_check unsigned long
> > >  _copy_from_user(void *to, const void __user *from, unsigned long n)
> > >  {
> > > -       unsigned long res = n;
> > > +       unsigned long res = n, to_copy = n;
> > > +
> > >         might_fault();
> > >         if (likely(access_ok(from, n))) {
> > >                 kasan_check_write(to, n);
> > >                 res = raw_copy_from_user(to, from, n);
> > > +               kmsan_unpoison_shadow(to, to_copy - res);
> > >         }
> > >         if (unlikely(res))
> > >                 memset(to + (n - res), 0, res);
> > > @@ -125,10 +144,13 @@ _copy_from_user(void *, const void __user *, unsigned long);
> > >  static inline __must_check unsigned long
> > >  _copy_to_user(void __user *to, const void *from, unsigned long n)
> > >  {
> > > +       unsigned long to_copy = n;
> > > +
> > >         might_fault();
> > >         if (access_ok(to, n)) {
> > >                 kasan_check_read(from, n);
> > >                 n = raw_copy_to_user(to, from, n);
> > > +               kmsan_copy_to_user(to, from, to_copy, n);
> > >         }
> > >         return n;
> > >  }
> > > diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> > > index 639d5e7014c1..f038676068b2 100644
> > > --- a/lib/iov_iter.c
> > > +++ b/lib/iov_iter.c
> > > @@ -137,18 +137,24 @@
> > >
> > >  static int copyout(void __user *to, const void *from, size_t n)
> > >  {
> > > +       size_t to_copy = n;
> > > +
> > >         if (access_ok(to, n)) {
> > >                 kasan_check_read(from, n);
> > >                 n = raw_copy_to_user(to, from, n);
> > > +               kmsan_copy_to_user(to, from, to_copy, n);
> > >         }
> > >         return n;
> > >  }
> > >
> > >  static int copyin(void *to, const void __user *from, size_t n)
> > >  {
> > > +       size_t to_copy = n;
> > > +
> > >         if (access_ok(from, n)) {
> > >                 kasan_check_write(to, n);
> > >                 n = raw_copy_from_user(to, from, n);
> > > +               kmsan_unpoison_shadow(to, to_copy - n);
> > >         }
> > >         return n;
> > >  }
> > > diff --git a/lib/usercopy.c b/lib/usercopy.c
> > > index cbb4d9ec00f2..abfd93edecba 100644
> > > --- a/lib/usercopy.c
> > > +++ b/lib/usercopy.c
> > > @@ -1,4 +1,5 @@
> > >  // SPDX-License-Identifier: GPL-2.0
> > > +#include <linux/kmsan-checks.h>
> > >  #include <linux/uaccess.h>
> > >  #include <linux/bitops.h>
> > >
> > > @@ -7,11 +8,12 @@
> > >  #ifndef INLINE_COPY_FROM_USER
> > >  unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n)
> > >  {
> > > -       unsigned long res = n;
> > > +       unsigned long res = n, to_copy = n;
> > >         might_fault();
> > >         if (likely(access_ok(from, n))) {
> > >                 kasan_check_write(to, n);
> > >                 res = raw_copy_from_user(to, from, n);
> > > +               kmsan_unpoison_shadow(to, to_copy - res);
> > >         }
> > >         if (unlikely(res))
> > >                 memset(to + (n - res), 0, res);
> > > @@ -23,10 +25,12 @@ EXPORT_SYMBOL(_copy_from_user);
> > >  #ifndef INLINE_COPY_TO_USER
> > >  unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
> > >  {
> > > +       unsigned long to_copy = n;
> > >         might_fault();
> > >         if (likely(access_ok(to, n))) {
> > >                 kasan_check_read(from, n);
> > >                 n = raw_copy_to_user(to, from, n);
> > > +               kmsan_copy_to_user(to, from, to_copy, n);
> > >         }
> > >         return n;
> > >  }
> > > --
> > > 2.24.0.432.g9d3f5f5b63-goog
> > >
>
>
>
> --
> Alexander Potapenko
> Software Engineer
>
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
>
> Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg