On 10/20/2014 06:54 AM, Andrey Ryabinin wrote:
>
> UBSan uses compile-time instrumentation to catch undefined behavior (UB).
> Compiler inserts code that perform certain kinds of
> checks before operations that could cause UB.
> If check fails (i.e. UB detected) __ubsan_handle_* function called.
> to print error message.
>
> So the most of the work is done by compiler.
> This patch just implements ubsan handlers printing errors.
>
> GCC supports this since 4.9, however upcoming GCC 5.0 has
> more checkers implemented.
>
> Different kinds of checks could be enabled via boot parameter:
> ubsan_handle=OEAINVBSLF.
> If ubsan_handle not present in cmdline default options are used: ELNVBSLF
>
> O - different kinds of overflows
> E - negation overflow, division overflow, division by zero.
> A - misaligned memory access.
> I - load from/store to an object with insufficient space.
> N - null argument declared with nonnull attribute,
> returned null from function which never returns null, null ptr dereference.
> V - variable size array with non-positive length
> B - out-of-bounds accesses.
> S - shifting out-of-bounds.
> L - load of invalid value (value out of range for the enum type, loading other then 0/1 to bool type)
> F - call to function through pointer with incorrect function type
> (AFAIK this is not implemented in gcc yet, probably works with clang, though
> I didn't check ubsan with clang at all).
>
> Instrumentation in kernel/printk/printk.c is disabled because struct printk_log is not properly aligned,
> therefore we are recursively taking logbuf_lock while trying to print error in __ubsan_handle*().
>
> Signed-off-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
> ---
> Makefile | 12 +-
> arch/x86/Kconfig | 1 +
> arch/x86/boot/Makefile | 1 +
> arch/x86/boot/compressed/Makefile | 1 +
> arch/x86/realmode/rm/Makefile | 1 +
> arch/x86/vdso/Makefile | 2 +
> drivers/firmware/efi/libstub/Makefile | 1 +
> include/linux/sched.h | 4 +
> kernel/printk/Makefile | 1 +
> lib/Kconfig.debug | 23 ++
> lib/Makefile | 3 +
> lib/ubsan.c | 559 ++++++++++++++++++++++++++++++++++
> lib/ubsan.h | 84 +++++
> scripts/Makefile.lib | 6 +
> 14 files changed, 698 insertions(+), 1 deletion(-)
> create mode 100644 lib/ubsan.c
> create mode 100644 lib/ubsan.h
>
> diff --git a/Makefile b/Makefile
> index 05d67af..d3e23f9 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -377,6 +377,9 @@ LDFLAGS_MODULE =
> CFLAGS_KERNEL =
> AFLAGS_KERNEL =
> CFLAGS_GCOV = -fprofile-arcs -ftest-coverage
> +CFLAGS_UBSAN = $(call cc-option, -fsanitize=undefined) \
> + $(call cc-option, -fno-sanitize=unreachable) \
> + $(call cc-option, -fno-sanitize=float-cast-overflow)
What's the reason behind those two -fno-sanitize?
[snip]
> +config HAVE_ARCH_UBSAN_SANTIZE_ALL
> + bool
> +
> +config UBSAN
> + bool "Undefined behaviour sanity checker"
> + help
> + This option enables undefined behaviour sanity checker
> + Compile-time instrumentataion used to detect various undefined
instrumentation
> + behaviours in runtime. Different kinds of checks could be enabled
> + via boot parameter ubsan_handle (see: Documentation/ubsan.txt).
> + (TODO: write docs).
> +
> +config UBSAN_SANITIZE_ALL
> + bool "Enable instrumentation for the entire kernel"
> + depends on UBSAN
> + depends on HAVE_ARCH_UBSAN_SANTIZE_ALL
> + default y
> + help
> + This option acitivates instrumentation for the entire kernel.
activates
> + If you don't enable this option, you have to explicitly specify
> + UBSAN_SANITIZE := y for the files/directories you want to check for UB.
> +
> +
[snip
> +/* By default enable everything except signed overflows and
> + * misaligned accesses
> + */
Why those two are disabled? Maybe we should be fixing them rather
than ignoring?
> +static unsigned long ubsan_handle = GENMASK(HANDLERS_END, 0) &
> + ~(BIT_MASK(SUM_OVERFLOW) | BIT_MASK(SUB_OVERFLOW) |
> + BIT_MASK(NEG_OVERFLOW) | BIT_MASK(ALIGNMENT));
> +
> +static void enable_handler(unsigned int handler)
> +{
> + set_bit(handler, &ubsan_handle);
> +}
> +
> +static bool handler_enabled(unsigned int handler)
> +{
> + return test_bit(handler, &ubsan_handle);
> +}
> +
> +#define REPORTED_BIT 31
> +#define COLUMN_MASK (~(1U << REPORTED_BIT))
> +
> +static bool is_disabled(struct source_location *location)
> +{
> + return test_and_set_bit(REPORTED_BIT,
> + (unsigned long *)&location->column);
> +}
> +
> +static void print_source_location(const char *prefix, struct source_location *loc)
> +{
> + pr_err("%s %s:%d:%d\n", prefix, loc->file_name,
> + loc->line, loc->column & COLUMN_MASK);
> +}
> +
> +static bool type_is_int(struct type_descriptor *type)
> +{
> + return type->type_kind == type_kind_int;
> +}
> +
> +static bool type_is_signed(struct type_descriptor *type)
> +{
> + return type_is_int(type) && (type->type_info & 1);
> +}
> +
> +static unsigned type_bit_width(struct type_descriptor *type)
> +{
> + return 1 << (type->type_info >> 1);
> +}
> +
> +static bool is_inline_int(struct type_descriptor *type)
> +{
> + unsigned inline_bits = sizeof(unsigned long)*8;
> + unsigned bits = type_bit_width(type);
> +
Shouldn't we check type_is_int() here as well?
> + return bits <= inline_bits;
> +}
[snip]
> +void __ubsan_handle_negate_overflow(struct overflow_data *data,
> + unsigned long old_val)
> +{
> +
> + char old_val_str[60];
> +
> + if (!handler_enabled(NEG_OVERFLOW))
> + return;
> +
> + if (current->in_ubsan)
> + return;
> +
> + if (is_disabled(&data->location))
> + return;
This pattern of 3 if()s is repeating itself couple of times, maybe
it deserves a function of it's own?
> + ubsan_prologue(&data->location);
> +
> + 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);
Thanks,
Sasha
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