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SubjectRe: mmotm 2019-04-19-14-53 uploaded (objtool)
On Fri, Apr 19, 2019 at 09:36:46PM -0700, Randy Dunlap wrote:
> On 4/19/19 2:53 PM, akpm@linux-foundation.org wrote:
> > The mm-of-the-moment snapshot 2019-04-19-14-53 has been uploaded to
> >
> > http://www.ozlabs.org/~akpm/mmotm/
> >
> > mmotm-readme.txt says
> >
> > README for mm-of-the-moment:
> >
> > http://www.ozlabs.org/~akpm/mmotm/
> >
> > This is a snapshot of my -mm patch queue. Uploaded at random hopefully
> > more than once a week.
>
> on x86_64:
>
> CC lib/strncpy_from_user.o
> lib/strncpy_from_user.o: warning: objtool: strncpy_from_user()+0x315: call to __ubsan_handle_add_overflow() with UACCESS enabled
> CC lib/strnlen_user.o
> lib/strnlen_user.o: warning: objtool: strnlen_user()+0x337: call to __ubsan_handle_sub_overflow() with UACCESS enabled

Lemme guess, you're using GCC < 8 ? That had a bug where UBSAN
considered signed overflow UB when using -fno-strict-overflow or
-fwrapv.

Now, we could of course allow this symbol, but I found only the below
was required to make allyesconfig build without issue.

Andy, Linus?

(note: the __put_user thing is from this one:

drivers/gpu/drm/i915/i915_gem_execbuffer.c: if (unlikely(__put_user(offset, &urelocs[r-stack].presumed_offset))) {

where (ptr) ends up non-trivial due to UBSAN)

---

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 22ba683afdc2..c82abd6e4ca3 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -427,10 +427,11 @@ do { \
({ \
__label__ __pu_label; \
int __pu_err = -EFAULT; \
- __typeof__(*(ptr)) __pu_val; \
- __pu_val = x; \
+ __typeof__(*(ptr)) __pu_val = (x); \
+ __typeof__(ptr) __pu_ptr = (ptr); \
+ __typeof__(size) __pu_size = (size); \
__uaccess_begin(); \
- __put_user_size(__pu_val, (ptr), (size), __pu_label); \
+ __put_user_size(__pu_val, __pu_ptr, __pu_size, __pu_label); \
__pu_err = 0; \
__pu_label: \
__uaccess_end(); \
diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
index 58eacd41526c..07045bc4872e 100644
--- a/lib/strncpy_from_user.c
+++ b/lib/strncpy_from_user.c
@@ -26,7 +26,7 @@
static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max)
{
const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
- long res = 0;
+ unsigned long res = 0;

/*
* Truncate 'max' to the user-specified limit, so that
diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
index 1c1a1b0e38a5..0729378ad3e9 100644
--- a/lib/strnlen_user.c
+++ b/lib/strnlen_user.c
@@ -28,7 +28,7 @@
static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
{
const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
- long align, res = 0;
+ unsigned long align, res = 0;
unsigned long c;

/*
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