[tip: x86/asm] ubsan, x86: Annotate and allow __ubsan_handle_shift_out_of_bounds() in uaccess regions

From: tip-bot2 for Peter Zijlstra
Date: Mon Oct 28 2019 - 07:42:22 EST

The following commit has been merged into the x86/asm branch of tip:

Commit-ID: 9a50dcaf0416a43e1fe411dc61a99c8333c90119
Gitweb: https://git.kernel.org/tip/9a50dcaf0416a43e1fe411dc61a99c8333c90119
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Mon, 21 Oct 2019 15:11:49 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Mon, 28 Oct 2019 10:43:00 +01:00

ubsan, x86: Annotate and allow __ubsan_handle_shift_out_of_bounds() in uaccess regions

The new check_zeroed_user() function uses variable shifts inside of a
user_access_begin()/user_access_end() section and that results in GCC
emitting __ubsan_handle_shift_out_of_bounds() calls, even though
through value range analysis it would be able to see that the UB in
question is impossible.

Annotate and whitelist this UBSAN function; continued use of
user_access_begin()/user_access_end() will undoubtedly result in
further uses of function.

Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Tested-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: cyphar@xxxxxxxxxx
Cc: keescook@xxxxxxxxxxxx
Cc: linux@xxxxxxxxxxxxxxxxxx
Fixes: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper")
Link: https://lkml.kernel.org/r/20191021131149.GA19358@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
lib/ubsan.c | 5 ++++-
tools/objtool/check.c | 1 +
2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/ubsan.c b/lib/ubsan.c
index e7d3173..0c46811 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -374,9 +374,10 @@ void __ubsan_handle_shift_out_of_bounds(struct shift_out_of_bounds_data *data,
struct type_descriptor *lhs_type = data->lhs_type;
char rhs_str[VALUE_LENGTH];
char lhs_str[VALUE_LENGTH];
+ unsigned long ua_flags = user_access_save();

if (suppress_report(&data->location))
- return;
+ goto out;

ubsan_prologue(&data->location, &flags);

@@ -402,6 +403,8 @@ void __ubsan_handle_shift_out_of_bounds(struct shift_out_of_bounds_data *data,

+ user_access_restore(ua_flags);

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 044c9a3..f53d3c5 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -481,6 +481,7 @@ static const char *uaccess_safe_builtin[] = {
+ "__ubsan_handle_shift_out_of_bounds",
/* misc */