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ubsan: disable UBSAN_DIV_ZERO for clang 

Building with UBSAN_DIV_ZERO with clang produces numerous fallthrough
warnings from objtool.

In the case of uncheck division, UBSAN_DIV_ZERO may introduce new
control flow to check for division by zero.

Because the result of the division is undefined, LLVM may optimize the
control flow such that after the call to __ubsan_handle_divrem_overflow
doesn't matter.  If panic_on_warn was set,
__ubsan_handle_divrem_overflow would panic.

The problem is is that panic_on_warn is run time configurable.  If it's
disabled, then we cannot guarantee that we will be able to recover
safely.  Disable this config for clang until we can come up with a
solution in LLVM.

Link: https://github.com/ClangBuiltLinux/linux/issues/1657
Link: https://github.com/llvm/llvm-project/issues/56289
Link: https://lore.kernel.org/lkml/CAHk-=wj1qhf7y3VNACEexyp5EbkNpdcu_542k-xZpzmYLOjiCg@mail.gmail.com/
Reported-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Desaulniers 2022-07-14 13:56:43 -07:00 committed by Linus Torvalds
parent b926f2adb0
commit e5d523f1ae
1 changed files with 3 additions and 0 deletions
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3
lib/Kconfig.ubsan
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@ -84,6 +84,9 @@ config UBSAN_SHIFT
config UBSAN_DIV_ZERO config UBSAN_DIV_ZERO
bool "Perform checking for integer divide-by-zero" bool "Perform checking for integer divide-by-zero"
depends on $(cc-option,-fsanitize=integer-divide-by-zero) depends on $(cc-option,-fsanitize=integer-divide-by-zero)
# https://github.com/ClangBuiltLinux/linux/issues/1657
# https://github.com/llvm/llvm-project/issues/56289
depends on !CC_IS_CLANG
help help
This option enables -fsanitize=integer-divide-by-zero which checks This option enables -fsanitize=integer-divide-by-zero which checks
for integer division by zero. This is effectively redundant with the for integer division by zero. This is effectively redundant with the