commit fad7cd3310db ("nbd: add the check to prevent overflow in
__nbd_ioctl()") raised an issue from the fallback helpers added in
commit f0907827a8a9 ("compiler.h: enable builtin overflow checkers and
add fallback code")
ERROR: modpost: "__divdi3" [drivers/block/nbd.ko] undefined!
As Stephen Rothwell notes:
The added check_mul_overflow() call is being passed 64 bit values.
COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW is not set for this build (see
include/linux/overflow.h).
Specifically, the helpers for checking whether the results of a
multiplication overflowed (__unsigned_mul_overflow,
__signed_add_overflow) use the division operator when
!COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW. This is problematic for 64b
operands on 32b hosts.
This was fixed upstream by
commit 76ae847497bc ("Documentation: raise minimum supported version of
GCC to 5.1")
which is not suitable to be backported to stable; I didn't have this
patch ready in time.
Cc: stable@xxxxxxxxxxxxxxx
Cc: Arnd Bergmann <arnd@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Suggested-by: Pavel Machek <pavel@xxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/1438
Link: https://lore.kernel.org/all/20210909182525.372ee687@xxxxxxxxxxxxxxxx/
Link: https://lore.kernel.org/lkml/20210910234047.1019925-1-ndesaulniers@xxxxxxxxxx/
Fixes: f0907827a8a9 ("compiler.h: enable builtin overflow checkers and
add fallback code")
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
---
This kind of generic meta-programming in C and my lack of experience in
doing so makes me very uncomfortable (and slightly ashamed) to send
this. I would appreciate careful review and feedback. I would appreciate
if Naresh can test this with GCC 4.9, which I don't have handy.
Linus also suggested I look into the use of _Generic; I haven't
evaluated that approach yet, but I felt like posting this early for
feedback.
include/linux/math64.h | 35 +++++++++++++++++++++++++++++++++++
include/linux/overflow.h | 8 ++++----
2 files changed, 39 insertions(+), 4 deletions(-)
diff --git a/include/linux/math64.h b/include/linux/math64.h
index 66deb1fdc2ef..bc9c12c168d0 100644
--- a/include/linux/math64.h
+++ b/include/linux/math64.h
@@ -10,6 +10,9 @@
#define div64_long(x, y) div64_s64((x), (y))
#define div64_ul(x, y) div64_u64((x), (y))
+#ifndef is_signed_type
+#define is_signed_type(type) (((type)(-1)) < (type)1)
+#endif
/**
* div_u64_rem - unsigned 64bit divide with 32bit divisor with remainder
@@ -111,6 +114,15 @@ extern s64 div64_s64(s64 dividend, s64 divisor);
#endif /* BITS_PER_LONG */
+#define div64_x64(dividend, divisor) ({ \
+ BUILD_BUG_ON_MSG(sizeof(dividend) < sizeof(u64),\
+ "prefer div_x64"); \
+ __builtin_choose_expr( \
+ is_signed_type(typeof(dividend)), \
+ div64_s64(dividend, divisor), \
+ div64_u64(dividend, divisor)); \
+})
+
/**
* div_u64 - unsigned 64bit divide with 32bit divisor
* @dividend: unsigned 64bit dividend
@@ -141,6 +153,29 @@ static inline s64 div_s64(s64 dividend, s32 divisor)
}
#endif
+#define div_x64(dividend, divisor) ({ \
+ BUILD_BUG_ON_MSG(sizeof(dividend) > sizeof(u32),\
+ "prefer div64_x64"); \
+ __builtin_choose_expr( \
+ is_signed_type(typeof(dividend)), \
+ div_s64(dividend, divisor), \
+ div_u64(dividend, divisor)); \
+})
+
+#define div_64(dividend, divisor) ({ \
+ BUILD_BUG_ON_MSG(sizeof(dividend) > sizeof(u64), \
+ "128b div unsupported"); \
+ __builtin_choose_expr( \
+ __builtin_types_compatible_p(typeof(dividend), s64) || \
+ __builtin_types_compatible_p(typeof(dividend), u64), \
+ __builtin_choose_expr( \
+ __builtin_types_compatible_p(typeof(divisor), s64) || \
+ __builtin_types_compatible_p(typeof(divisor), u64), \
+ div64_x64(dividend, divisor), \
+ div_x64(dividend, divisor)), \
+ dividend / divisor); \
+})
+
u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder);
#ifndef mul_u32_u32
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index ef74051d5cfe..2ebdf220c184 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -123,8 +123,8 @@ static inline bool __must_check __must_check_overflow(bool overflow)
(void) (&__a == __d); \
*__d = __a * __b; \
__builtin_constant_p(__b) ? \
- __b > 0 && __a > type_max(typeof(__a)) / __b : \
- __a > 0 && __b > type_max(typeof(__b)) / __a; \
+ __b > 0 && __a > div_64(type_max(typeof(__a)), __b) : \
+ __a > 0 && __b > div_64(type_max(typeof(__b)), __a); \
})
/*
@@ -195,8 +195,8 @@ static inline bool __must_check __must_check_overflow(bool overflow)
(void) (&__a == &__b); \
(void) (&__a == __d); \
*__d = (u64)__a * (u64)__b; \
- (__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \
- (__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \
+ (__b > 0 && (__a > div_64(__tmax, __b) || __a < div_64(__tmin, __b))) || \
+ (__b < (typeof(__b))-1 && (__a > div_64(__tmin, __b) || __a < div_64(__tmax, __b))) || \
(__b == (typeof(__b))-1 && __a == __tmin); \
})
--
2.33.0.309.g3052b89438-goog
