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@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: cyphar@cyphar.com
Cc: keescook@chromium.org
Cc: linux@rasmusvillemoes.dk
Fixes: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper")
Link: https://lkml.kernel.org/r/20191021131149.GA19358@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/lib/ubsan.c b/lib/ubsan.c
index e7d31735950de7c0980967164ce21ba0ca8b77c0..0c4681118fcd2a819aa3f5e09ba569c4bd87c20a 100644 (file)
--- 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,
                        lhs_type->type_name);
 
        ubsan_epilogue(&flags);
+out:
+       user_access_restore(ua_flags);
 }
 EXPORT_SYMBOL(__ubsan_handle_shift_out_of_bounds);
 

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 044c9a3cb2472354d3a78b77e43793e5a9043360..f53d3c515cdc0b6701059c5c5a8713f5729acad3 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -481,6 +481,7 @@ 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",