user/sven/linux.git/include/linux/overflow.h, branch v4.9.241

overflow: Include header file with SIZE_MAX declaration

2020-10-29T08:05:39Z

[ Upstream commit a4947e84f23474803b62a2759b5808147e4e15f9 ] The various array_size functions use SIZE_MAX define, but missed limits.h causes to failure to compile code that needs overflow.h. In file included from drivers/infiniband/core/uverbs_std_types_device.c:6: ./include/linux/overflow.h: In function 'array_size': ./include/linux/overflow.h:258:10: error: 'SIZE_MAX' undeclared (first use in this function) 258 | return SIZE_MAX; | ^~~~~~~~ Fixes: 610b15c50e86 ("overflow.h: Add allocation size calculation helpers") Link: https://lore.kernel.org/r/20200913102928.134985-1-leon@kernel.org Signed-off-by: Leon Romanovsky Signed-off-by: Jason Gunthorpe Signed-off-by: Sasha Levin

overflow.h: Add allocation size calculation helpers

2020-09-03T09:21:22Z

commit 610b15c50e86eb1e4b77274fabcaea29ac72d6a8 upstream. In preparation for replacing unchecked overflows for memory allocations, this creates helpers for the 3 most common calculations: array_size(a, b): 2-dimensional array array3_size(a, b, c): 3-dimensional array struct_size(ptr, member, n): struct followed by n-many trailing members Each of these return SIZE_MAX on overflow instead of wrapping around. (Additionally renames a variable named "array_size" to avoid future collision.) Co-developed-by: Matthew Wilcox Signed-off-by: Kees Cook Signed-off-by: Greg Kroah-Hartman

overflow.h: Add arithmetic shift helper

2020-05-02T15:23:10Z

commit 0c66847793d1982d1083dc6f7adad60fa265ce9c upstream. Add shift_overflow() helper to assist driver authors in ensuring that shift operations don't cause overflows or other odd conditions. Signed-off-by: Jason Gunthorpe Signed-off-by: Leon Romanovsky [kees: tweaked comments and commit log, dropped unneeded assignment] Signed-off-by: Kees Cook Signed-off-by: Greg Kroah-Hartman

compiler.h: enable builtin overflow checkers and add fallback code

2019-01-31T07:12:35Z

commit f0907827a8a9152aedac2833ed1b674a7b2a44f2 upstream. This adds wrappers for the __builtin overflow checkers present in gcc 5.1+ as well as fallback implementations for earlier compilers. It's not that easy to implement the fully generic __builtin_X_overflow(T1 a, T2 b, T3 *d) in macros, so the fallback code assumes that T1, T2 and T3 are the same. We obviously don't want the wrappers to have different semantics depending on $GCC_VERSION, so we also insist on that even when using the builtins. There are a few problems with the 'a+b < a' idiom for checking for overflow: For signed types, it relies on undefined behaviour and is not actually complete (it doesn't check underflow; e.g. INT_MIN+INT_MIN == 0 isn't caught). Due to type promotion it is wrong for all types (signed and unsigned) narrower than int. Similarly, when a and b does not have the same type, there are subtle cases like u32 a; if (a + sizeof(foo) < a) return -EOVERFLOW; a += sizeof(foo); where the test is always false on 64 bit platforms. Add to that that it is not always possible to determine the types involved at a glance. The new overflow.h is somewhat bulky, but that's mostly a result of trying to be type-generic, complete (e.g. catching not only overflow but also signed underflow) and not relying on undefined behaviour. Linus is of course right [1] that for unsigned subtraction a-b, the right way to check for overflow (underflow) is "b > a" and not "__builtin_sub_overflow(a, b, &d)", but that's just one out of six cases covered here, and included mostly for completeness. So is it worth it? I think it is, if nothing else for the documentation value of seeing if (check_add_overflow(a, b, &d)) return -EGOAWAY; do_stuff_with(d); instead of the open-coded (and possibly wrong and/or incomplete and/or UBsan-tickling) if (a+b < a) return -EGOAWAY; do_stuff_with(a+b); While gcc does recognize the 'a+b < a' idiom for testing unsigned add overflow, it doesn't do nearly as good for unsigned multiplication (there's also no single well-established idiom). So using check_mul_overflow in kcalloc and friends may also make gcc generate slightly better code. [1] https://lkml.org/lkml/2015/11/2/658 Signed-off-by: Rasmus Villemoes Signed-off-by: Kees Cook Signed-off-by: Greg Kroah-Hartman