| Message ID | 20240123002814.1396804-73-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | overflow: Refactor open-coded arithmetic wrap-around | expand |
Hello Kees, On Mon, 2024-01-22 at 16:27 -0800, Kees Cook wrote: > In an effort to separate intentional arithmetic wrap-around from > unexpected wrap-around, we need to refactor places that depend on this > kind of math. One of the most common code patterns of this is: > > VAR + value < VAR > > Notably, this is considered "undefined behavior" for signed and pointer > types, which the kernel works around by using the -fno-strict-overflow > option in the build[1] (which used to just be -fwrapv). Regardless, we > want to get the kernel source to the position where we can meaningfully > instrument arithmetic wrap-around conditions and catch them when they > are unexpected, regardless of whether they are signed[2], unsigned[3], > or pointer[4] types. > > Refactor open-coded wrap-around addition test to use add_would_overflow(). > This paves the way to enabling the wrap-around sanitizers in the future. > > Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] > Link: https://github.com/KSPP/linux/issues/26 [2] > Link: https://github.com/KSPP/linux/issues/27 [3] > Link: https://github.com/KSPP/linux/issues/344 [4] > Cc: Yoshinori Sato <ysato@users.sourceforge.jp> > Cc: Rich Felker <dalias@libc.org> > Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> > Cc: linux-sh@vger.kernel.org > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > arch/sh/kernel/sys_sh.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/sh/kernel/sys_sh.c b/arch/sh/kernel/sys_sh.c > index a5a7b33ed81a..e390caeb8c00 100644 > --- a/arch/sh/kernel/sys_sh.c > +++ b/arch/sh/kernel/sys_sh.c > @@ -66,7 +66,7 @@ asmlinkage int sys_cacheflush(unsigned long addr, unsigned long len, int op) > * Verify that the specified address region actually belongs > * to this process. > */ > - if (addr + len < addr) > + if (add_would_overflow(addr, len)) > return -EFAULT; > > mmap_read_lock(current->mm); Sounds like a very sensible change to me. Acked-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> Adrian
diff --git a/arch/sh/kernel/sys_sh.c b/arch/sh/kernel/sys_sh.c index a5a7b33ed81a..e390caeb8c00 100644 --- a/arch/sh/kernel/sys_sh.c +++ b/arch/sh/kernel/sys_sh.c @@ -66,7 +66,7 @@ asmlinkage int sys_cacheflush(unsigned long addr, unsigned long len, int op) * Verify that the specified address region actually belongs * to this process. */ - if (addr + len < addr) + if (add_would_overflow(addr, len)) return -EFAULT; mmap_read_lock(current->mm);
In an effort to separate intentional arithmetic wrap-around from unexpected wrap-around, we need to refactor places that depend on this kind of math. One of the most common code patterns of this is: VAR + value < VAR Notably, this is considered "undefined behavior" for signed and pointer types, which the kernel works around by using the -fno-strict-overflow option in the build[1] (which used to just be -fwrapv). Regardless, we want to get the kernel source to the position where we can meaningfully instrument arithmetic wrap-around conditions and catch them when they are unexpected, regardless of whether they are signed[2], unsigned[3], or pointer[4] types. Refactor open-coded wrap-around addition test to use add_would_overflow(). This paves the way to enabling the wrap-around sanitizers in the future. Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] Link: https://github.com/KSPP/linux/issues/26 [2] Link: https://github.com/KSPP/linux/issues/27 [3] Link: https://github.com/KSPP/linux/issues/344 [4] Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Rich Felker <dalias@libc.org> Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> Cc: linux-sh@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/sh/kernel/sys_sh.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)