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Subject[PATCH] ubsan: remove overflow checks
Date
Since GCC 8.0 -fsanitize=signed-integer-overflow doesn't work with -fwrapv.
-fwrapv makes signed overflows defines and GCC essentially disables
ubsan checks. On GCC < 8.0 -fwrapv doesn't have influence on
-fsanitize=signed-integer-overflow setting, so it kinda works
but generates false-positves and violates uaccess rules:

lib/iov_iter.o: warning: objtool: iovec_from_user()+0x22d: call to __ubsan_handle_add_overflow() with UACCESS enabled

Disable signed overflow checks to avoid these problems.
Remove unsigned overflow checks as well.
Unsigned overflow appeared as side effect of the commit
cdf8a76fda4a ("ubsan: move cc-option tests into Kconfig"),
but it never worked (kernel doesn't boot). And unsigned overflows
are allowed by C standard, so it just pointless.

Signed-off-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
---
lib/Kconfig.ubsan | 17 -----------
lib/test_ubsan.c | 49 ------------------------------
lib/ubsan.c | 68 ------------------------------------------
scripts/Makefile.ubsan | 2 --
4 files changed, 136 deletions(-)

diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index 3a0b1c930733..e5372a13511d 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -112,23 +112,6 @@ config UBSAN_UNREACHABLE
This option enables -fsanitize=unreachable which checks for control
flow reaching an expected-to-be-unreachable position.

-config UBSAN_SIGNED_OVERFLOW
- bool "Perform checking for signed arithmetic overflow"
- default UBSAN
- depends on $(cc-option,-fsanitize=signed-integer-overflow)
- help
- This option enables -fsanitize=signed-integer-overflow which checks
- for overflow of any arithmetic operations with signed integers.
-
-config UBSAN_UNSIGNED_OVERFLOW
- bool "Perform checking for unsigned arithmetic overflow"
- depends on $(cc-option,-fsanitize=unsigned-integer-overflow)
- depends on !X86_32 # avoid excessive stack usage on x86-32/clang
- help
- This option enables -fsanitize=unsigned-integer-overflow which checks
- for overflow of any arithmetic operations with unsigned integers. This
- currently causes x86 to fail to boot.
-
config UBSAN_OBJECT_SIZE
bool "Perform checking for accesses beyond the end of objects"
default UBSAN
diff --git a/lib/test_ubsan.c b/lib/test_ubsan.c
index 5e5d9355ef49..7e7bbd0f3fd2 100644
--- a/lib/test_ubsan.c
+++ b/lib/test_ubsan.c
@@ -11,51 +11,6 @@ typedef void(*test_ubsan_fp)(void);
#config, IS_ENABLED(config) ? "y" : "n"); \
} while (0)

-static void test_ubsan_add_overflow(void)
-{
- volatile int val = INT_MAX;
- volatile unsigned int uval = UINT_MAX;
-
- UBSAN_TEST(CONFIG_UBSAN_SIGNED_OVERFLOW);
- val += 2;
-
- UBSAN_TEST(CONFIG_UBSAN_UNSIGNED_OVERFLOW);
- uval += 2;
-}
-
-static void test_ubsan_sub_overflow(void)
-{
- volatile int val = INT_MIN;
- volatile unsigned int uval = 0;
- volatile int val2 = 2;
-
- UBSAN_TEST(CONFIG_UBSAN_SIGNED_OVERFLOW);
- val -= val2;
-
- UBSAN_TEST(CONFIG_UBSAN_UNSIGNED_OVERFLOW);
- uval -= val2;
-}
-
-static void test_ubsan_mul_overflow(void)
-{
- volatile int val = INT_MAX / 2;
- volatile unsigned int uval = UINT_MAX / 2;
-
- UBSAN_TEST(CONFIG_UBSAN_SIGNED_OVERFLOW);
- val *= 3;
-
- UBSAN_TEST(CONFIG_UBSAN_UNSIGNED_OVERFLOW);
- uval *= 3;
-}
-
-static void test_ubsan_negate_overflow(void)
-{
- volatile int val = INT_MIN;
-
- UBSAN_TEST(CONFIG_UBSAN_SIGNED_OVERFLOW);
- val = -val;
-}
-
static void test_ubsan_divrem_overflow(void)
{
volatile int val = 16;
@@ -155,10 +110,6 @@ static void test_ubsan_object_size_mismatch(void)
}

static const test_ubsan_fp test_ubsan_array[] = {
- test_ubsan_add_overflow,
- test_ubsan_sub_overflow,
- test_ubsan_mul_overflow,
- test_ubsan_negate_overflow,
test_ubsan_shift_out_of_bounds,
test_ubsan_out_of_bounds,
test_ubsan_load_invalid_value,
diff --git a/lib/ubsan.c b/lib/ubsan.c
index bec38c64d6a6..26229973049d 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -163,74 +163,6 @@ static void ubsan_epilogue(void)
}
}

-static void handle_overflow(struct overflow_data *data, void *lhs,
- void *rhs, char op)
-{
-
- struct type_descriptor *type = data->type;
- char lhs_val_str[VALUE_LENGTH];
- char rhs_val_str[VALUE_LENGTH];
-
- if (suppress_report(&data->location))
- return;
-
- ubsan_prologue(&data->location, type_is_signed(type) ?
- "signed-integer-overflow" :
- "unsigned-integer-overflow");
-
- val_to_string(lhs_val_str, sizeof(lhs_val_str), type, lhs);
- val_to_string(rhs_val_str, sizeof(rhs_val_str), type, rhs);
- pr_err("%s %c %s cannot be represented in type %s\n",
- lhs_val_str,
- op,
- rhs_val_str,
- type->type_name);
-
- ubsan_epilogue();
-}
-
-void __ubsan_handle_add_overflow(void *data,
- void *lhs, void *rhs)
-{
-
- handle_overflow(data, lhs, rhs, '+');
-}
-EXPORT_SYMBOL(__ubsan_handle_add_overflow);
-
-void __ubsan_handle_sub_overflow(void *data,
- void *lhs, void *rhs)
-{
- handle_overflow(data, lhs, rhs, '-');
-}
-EXPORT_SYMBOL(__ubsan_handle_sub_overflow);
-
-void __ubsan_handle_mul_overflow(void *data,
- void *lhs, void *rhs)
-{
- handle_overflow(data, lhs, rhs, '*');
-}
-EXPORT_SYMBOL(__ubsan_handle_mul_overflow);
-
-void __ubsan_handle_negate_overflow(void *_data, void *old_val)
-{
- struct overflow_data *data = _data;
- char old_val_str[VALUE_LENGTH];
-
- if (suppress_report(&data->location))
- return;
-
- ubsan_prologue(&data->location, "negation-overflow");
-
- val_to_string(old_val_str, sizeof(old_val_str), data->type, old_val);
-
- pr_err("negation of %s cannot be represented in type %s:\n",
- old_val_str, data->type->type_name);
-
- ubsan_epilogue();
-}
-EXPORT_SYMBOL(__ubsan_handle_negate_overflow);
-
-
void __ubsan_handle_divrem_overflow(void *_data, void *lhs, void *rhs)
{
struct overflow_data *data = _data;
diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
index 0e53a93e8f15..9e2092fd5206 100644
--- a/scripts/Makefile.ubsan
+++ b/scripts/Makefile.ubsan
@@ -8,8 +8,6 @@ ubsan-cflags-$(CONFIG_UBSAN_LOCAL_BOUNDS) += -fsanitize=local-bounds
ubsan-cflags-$(CONFIG_UBSAN_SHIFT) += -fsanitize=shift
ubsan-cflags-$(CONFIG_UBSAN_DIV_ZERO) += -fsanitize=integer-divide-by-zero
ubsan-cflags-$(CONFIG_UBSAN_UNREACHABLE) += -fsanitize=unreachable
-ubsan-cflags-$(CONFIG_UBSAN_SIGNED_OVERFLOW) += -fsanitize=signed-integer-overflow
-ubsan-cflags-$(CONFIG_UBSAN_UNSIGNED_OVERFLOW) += -fsanitize=unsigned-integer-overflow
ubsan-cflags-$(CONFIG_UBSAN_OBJECT_SIZE) += -fsanitize=object-size
ubsan-cflags-$(CONFIG_UBSAN_BOOL) += -fsanitize=bool
ubsan-cflags-$(CONFIG_UBSAN_ENUM) += -fsanitize=enum
--
2.26.2
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