Commit 7e3cf084 authored Oct 05, 2022 by Jason A. Donenfeld

treewide: use get_random_{u8,u16}() when possible, part 1



Rather than truncate a 32-bit value to a 16-bit value or an 8-bit value,
simply use the get_random_{u8,u16}() functions, which are faster than
wasting the additional bytes from a 32-bit value. This was done
mechanically with this coccinelle script:

@@
expression E;
identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32";
typedef u16;
typedef __be16;
typedef __le16;
typedef u8;
@@
(
- (get_random_u32() & 0xffff)
+ get_random_u16()
|
- (get_random_u32() & 0xff)
+ get_random_u8()
|
- (get_random_u32() % 65536)
+ get_random_u16()
|
- (get_random_u32() % 256)
+ get_random_u8()
|
- (get_random_u32() >> 16)
+ get_random_u16()
|
- (get_random_u32() >> 24)
+ get_random_u8()
|
- (u16)get_random_u32()
+ get_random_u16()
|
- (u8)get_random_u32()
+ get_random_u8()
|
- (__be16)get_random_u32()
+ (__be16)get_random_u16()
|
- (__le16)get_random_u32()
+ (__le16)get_random_u16()
|
- prandom_u32_max(65536)
+ get_random_u16()
|
- prandom_u32_max(256)
+ get_random_u8()
|
- E->inet_id = get_random_u32()
+ E->inet_id = get_random_u16()
)

@@
identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32";
typedef u16;
identifier v;
@@
- u16 v = get_random_u32();
+ u16 v = get_random_u16();

@@
identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32";
typedef u8;
identifier v;
@@
- u8 v = get_random_u32();
+ u8 v = get_random_u8();

@@
identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32";
typedef u16;
u16 v;
@@
-  v = get_random_u32();
+  v = get_random_u16();

@@
identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32";
typedef u8;
u8 v;
@@
-  v = get_random_u32();
+  v = get_random_u8();

// Find a potential literal
@literal_mask@
expression LITERAL;
type T;
identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32";
position p;
@@

        ((T)get_random_u32()@p & (LITERAL))

// Examine limits
@script:python add_one@
literal << literal_mask.LITERAL;
RESULT;
@@

value = None
if literal.startswith('0x'):
        value = int(literal, 16)
elif literal[0] in '123456789':
        value = int(literal, 10)
if value is None:
        print("I don't know how to handle %s" % (literal))
        cocci.include_match(False)
elif value < 256:
        coccinelle.RESULT = cocci.make_ident("get_random_u8")
elif value < 65536:
        coccinelle.RESULT = cocci.make_ident("get_random_u16")
else:
        print("Skipping large mask of %s" % (literal))
        cocci.include_match(False)

// Replace the literal mask with the calculated result.
@plus_one@
expression literal_mask.LITERAL;
position literal_mask.p;
identifier add_one.RESULT;
identifier FUNC;
@@

-       (FUNC()@p & (LITERAL))
+       (RESULT() & LITERAL)

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Yury Norov <yury.norov@gmail.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk> # for sch_cake
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

parent 8b3ccbc1

arch/arm/kernel/signal.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -655,7 +655,7 @@ struct page *get_signal_page(void)
		PAGE_SIZE / sizeof(u32));

		/* Give the signal return code some randomness */
		offset = 0x200 + (get_random_int() & 0x7fc);
		offset = 0x200 + (get_random_u16() & 0x7fc);
		signal_return_offset = offset;

		/* Copy signal return handlers into the page */

arch/arm64/kernel/syscall.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -67,7 +67,7 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
		*
		* The resulting 5 bits of entropy is seen in SP[8:4].
		*/
		choose_random_kstack_offset(get_random_int() & 0x1FF);
		choose_random_kstack_offset(get_random_u16() & 0x1FF);
		}

		static inline bool has_syscall_work(unsigned long flags)

crypto/testmgr.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -927,7 +927,7 @@ static void generate_random_bytes(u8 *buf, size_t count)
		b = 0xff;
		break;
		default:
		b = (u8)prandom_u32();
		b = get_random_u8();
		break;
		}
		memset(buf, b, count);
		@@ -935,8 +935,8 @@ static void generate_random_bytes(u8 *buf, size_t count)
		break;
		case 2:
		/* Ascending or descending bytes, plus optional mutations */
		increment = (u8)prandom_u32();
		b = (u8)prandom_u32();
		increment = get_random_u8();
		b = get_random_u8();
		for (i = 0; i < count; i++, b += increment)
		buf[i] = b;
		mutate_buffer(buf, count);
		@@ -944,7 +944,7 @@ static void generate_random_bytes(u8 *buf, size_t count)
		default:
		/* Fully random bytes */
		for (i = 0; i < count; i++)
		buf[i] = (u8)prandom_u32();
		buf[i] = get_random_u8();
		}
		}

drivers/media/common/v4l2-tpg/v4l2-tpg-core.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -870,7 +870,7 @@ static void precalculate_color(struct tpg_data *tpg, int k)
		g = tpg_colors[col].g;
		b = tpg_colors[col].b;
		} else if (tpg->pattern == TPG_PAT_NOISE) {
		r = g = b = prandom_u32_max(256);
		r = g = b = get_random_u8();
		} else if (k == TPG_COLOR_RANDOM) {
		r = g = b = tpg->qual_offset + prandom_u32_max(196);
		} else if (k >= TPG_COLOR_RAMP) {

drivers/media/test-drivers/vivid/vivid-radio-rx.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -104,8 +104,8 @@ ssize_t vivid_radio_rx_read(struct file file, char __user buf,
		break;
		case 2:
		rds.block \|= V4L2_RDS_BLOCK_ERROR;
		rds.lsb = prandom_u32_max(256);
		rds.msb = prandom_u32_max(256);
		rds.lsb = get_random_u8();
		rds.msb = get_random_u8();
		break;
		case 3: /* Skip block altogether */
		if (i)