On Mon, Sep 13, 2021 at 05:23:18PM -0700, Nick Desaulniers wrote:
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@vger.kernel.org Cc: Kees Cook keescook@chromium.org Cc: Rasmus Villemoes linux@rasmusvillemoes.dk Reported-by: Naresh Kamboju naresh.kamboju@linaro.org Reported-by: Nathan Chancellor nathan@kernel.org Reported-by: Stephen Rothwell sfr@canb.auug.org.au Suggested-by: Linus Torvalds torvalds@linux-foundation.org Suggested-by: Pavel Machek pavel@ucw.cz Link: https://lore.kernel.org/all/20210909182525.372ee687@canb.auug.org.au/ Link: https://github.com/ClangBuiltLinux/linux/issues/1438 Fixes: f0907827a8a9 ("compiler.h: enable builtin overflow checkers and add fallback code") Signed-off-by: Nick Desaulniers ndesaulniers@google.com
Changes v1 -> v2:
- Change the BUILD_BUG_ON_MSG's to check the divisor! Not the dividend!
- Change __builtin_choose_expr/__builtin_constant_p soup to _Generic as per Linus.
- Add Linus' Suggested-by.
- use __ prefixes on new macros.
- add parens around use of macro parameters.
- realign trailing .
Note to Rasmus: I did not include comments on the usage. I don't think we really intend for folks to be using these, much less so in -stable.
include/linux/math64.h | 37 +++++++++++++++++++++++++++++++++++++ include/linux/overflow.h | 8 ++++---- 2 files changed, 41 insertions(+), 4 deletions(-)
diff --git a/include/linux/math64.h b/include/linux/math64.h index 66deb1fdc2ef..a1a6ad98b5ea 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(divisor) < 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 +153,31 @@ static inline s64 div_s64(s64 dividend, s32 divisor) } #endif +#define __div_x64(dividend, divisor) ({ \
- BUILD_BUG_ON_MSG(sizeof(divisor) > 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) \
- _Generic((divisor), \
- s64: __div64_x64((dividend), (divisor)), \
- u64: __div64_x64((dividend), (divisor)), \
- default: __div_x64((dividend), (divisor)))
+#define div_64(dividend, divisor) ({ \
- BUILD_BUG_ON_MSG(sizeof(dividend) > sizeof(u64) || \
sizeof(divisor) > sizeof(u64), \"128b div unsupported"); \- _Generic((dividend), \
- s64: __div_64((dividend), (divisor)), \
- u64: __div_64((dividend), (divisor)), \
- default: (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); \
})
base-commit: cb83afdc0b865d7c8a74d2b2a1f7dd393e1d196d
2.33.0.309.g3052b89438-goog
Why is this needed in the 5.10.y tree? I see that commit fad7cd3310db ("nbd: add the check to prevent overflow in __nbd_ioctl()") is planned to go into 5.14.y and 5.13.y, but no further back at the moment.
confused,
greg k-h