linux-kernel - Re: linux-next: Tree for Oct 18 (objtool)

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Date:   Mon, 21 Oct 2019 15:11:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, linux@...musvillemoes.dk,
        cyphar@...har.com, keescook@...omium.org,
        christian.brauner@...ntu.com
Subject: Re: linux-next: Tree for Oct 18 (objtool)

On Mon, Oct 21, 2019 at 02:35:49PM +0200, Peter Zijlstra wrote:
> On Fri, Oct 18, 2019 at 08:33:11AM -0700, Randy Dunlap wrote:
> > On 10/18/19 12:03 AM, Stephen Rothwell wrote:
> > > Hi all,
> > > 
> > > Changes since 20191017:
> > > 
> > 
> > on x86_64:
> > lib/usercopy.o: warning: objtool: check_zeroed_user()+0x35f: call to __ubsan_handle_shift_out_of_bounds() with UACCESS enabled
> 
> Blergh... I suppose the below will fix that. I'm a bit conflicted on it
> though, the alternative is annotating more ubsan crud.

By popular request; here's that alternative. Completely untested :-)

---
 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 39d5952c4273..0dce3ff45b5b 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -359,9 +359,10 @@ 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 flags = user_access_save();
 
 	if (suppress_report(&data->location))
-		return;
+		goto out;
 
 	ubsan_prologue(&data->location);
 
@@ -387,6 +388,8 @@ void __ubsan_handle_shift_out_of_bounds(struct shift_out_of_bounds_data *data,
 			lhs_type->type_name);
 
 	ubsan_epilogue();
+out:
+	user_access_restore(flags);
 }
 EXPORT_SYMBOL(__ubsan_handle_shift_out_of_bounds);
 
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 543c068096b1..4768d91c6d68 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -482,6 +482,7 @@ static const char *uaccess_safe_builtin[] = {
 	"ubsan_type_mismatch_common",
 	"__ubsan_handle_type_mismatch",
 	"__ubsan_handle_type_mismatch_v1",
+	"__ubsan_handle_shift_out_of_bounds",
 	/* misc */
 	"csum_partial_copy_generic",
 	"__memcpy_mcsafe",