treewide: use prandom_u32_max() when possible, part 1

Rather than incurring a division or requesting too many random bytes for
the given range, use the prandom_u32_max() function, which only takes
the minimum required bytes from the RNG and avoids divisions. This was
done mechanically with this coccinelle script:

@basic@
expression E;
type T;
identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32";
typedef u64;
@@
(
- ((T)get_random_u32() % (E))
+ prandom_u32_max(E)
|
- ((T)get_random_u32() & ((E) - 1))
+ prandom_u32_max(E * XXX_MAKE_SURE_E_IS_POW2)
|
- ((u64)(E) * get_random_u32() >> 32)
+ prandom_u32_max(E)
|
- ((T)get_random_u32() & ~PAGE_MASK)
+ prandom_u32_max(PAGE_SIZE)
)

@multi_line@
identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32";
identifier RAND;
expression E;
@@

-       RAND = get_random_u32();
        ... when != RAND
-       RAND %= (E);
+       RAND = prandom_u32_max(E);

// 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))

// Add one to the literal.
@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 == 2**32 - 1 or value == 2**31 - 1 or value == 2**24 - 1 or value == 2**16 - 1 or value == 2**8 - 1:
        print("Skipping 0x%x for cleanup elsewhere" % (value))
        cocci.include_match(False)
elif value & (value + 1) != 0:
        print("Skipping 0x%x because it's not a power of two minus one" % (value))
        cocci.include_match(False)
elif literal.startswith('0x'):
        coccinelle.RESULT = cocci.make_expr("0x%x" % (value + 1))
else:
        coccinelle.RESULT = cocci.make_expr("%d" % (value + 1))

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

-       (FUNC()@p & (LITERAL))
+       prandom_u32_max(RESULT)

@collapse_ret@
type T;
identifier VAR;
expression E;
@@

 {
-       T VAR;
-       VAR = (E);
-       return VAR;
+       return E;
 }

@drop_var@
type T;
identifier VAR;
@@

 {
-       T VAR;
        ... when != VAR
 }

Reviewed-by: Greg Kroah-Hartman <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Reviewed-by: Yury Norov <[email protected]>
Reviewed-by: KP Singh <[email protected]>
Reviewed-by: Jan Kara <[email protected]> # for ext4 and sbitmap
Reviewed-by: Christoph Böhmwalder <[email protected]> # for drbd
Acked-by: Jakub Kicinski <[email protected]>
Acked-by: Heiko Carstens <[email protected]> # for s390
Acked-by: Ulf Hansson <[email protected]> # for mmc
Acked-by: Darrick J. Wong <[email protected]> # for xfs
Signed-off-by: Jason A. Donenfeld <[email protected]>

Author: zx2c4

arch/arm/kernel/process.c

@@ -375,7 +375,7 @@ static unsigned long sigpage_addr(const struct mm_struct *mm,
 
 	slots = ((last - first) >> PAGE_SHIFT) + 1;
 
-	offset = get_random_int() % slots;
+	offset = prandom_u32_max(slots);
 
 	addr = first + (offset << PAGE_SHIFT);
 

arch/arm64/kernel/process.c

@@ -595,7 +595,7 @@ unsigned long __get_wchan(struct task_struct *p)
 unsigned long arch_align_stack(unsigned long sp)
 {
 	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
-		sp -= get_random_int() & ~PAGE_MASK;
+		sp -= prandom_u32_max(PAGE_SIZE);
 	return sp & ~0xf;
 }
 

arch/loongarch/kernel/process.c

@@ -293,7 +293,7 @@ unsigned long stack_top(void)
 unsigned long arch_align_stack(unsigned long sp)
 {
 	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
-		sp -= get_random_int() & ~PAGE_MASK;
+		sp -= prandom_u32_max(PAGE_SIZE);
 
 	return sp & STACK_ALIGN;
 }

arch/loongarch/kernel/vdso.c

@@ -78,7 +78,7 @@ static unsigned long vdso_base(void)
 	unsigned long base = STACK_TOP;
 
 	if (current->flags & PF_RANDOMIZE) {
-		base += get_random_int() & (VDSO_RANDOMIZE_SIZE - 1);
+		base += prandom_u32_max(VDSO_RANDOMIZE_SIZE);
 		base = PAGE_ALIGN(base);
 	}
 

arch/mips/kernel/process.c

@@ -711,7 +711,7 @@ unsigned long mips_stack_top(void)
 unsigned long arch_align_stack(unsigned long sp)
 {
 	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
-		sp -= get_random_int() & ~PAGE_MASK;
+		sp -= prandom_u32_max(PAGE_SIZE);
 
 	return sp & ALMASK;
 }

arch/mips/kernel/vdso.c

@@ -79,7 +79,7 @@ static unsigned long vdso_base(void)
 	}
 
 	if (current->flags & PF_RANDOMIZE) {
-		base += get_random_int() & (VDSO_RANDOMIZE_SIZE - 1);
+		base += prandom_u32_max(VDSO_RANDOMIZE_SIZE);
 		base = PAGE_ALIGN(base);
 	}
 

arch/parisc/kernel/vdso.c

@@ -75,7 +75,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
 
 	map_base = mm->mmap_base;
 	if (current->flags & PF_RANDOMIZE)
-		map_base -= (get_random_int() & 0x1f) * PAGE_SIZE;
+		map_base -= prandom_u32_max(0x20) * PAGE_SIZE;
 
 	vdso_text_start = get_unmapped_area(NULL, map_base, vdso_text_len, 0, 0);
 

arch/powerpc/kernel/process.c

@@ -2308,6 +2308,6 @@ void notrace __ppc64_runlatch_off(void)
 unsigned long arch_align_stack(unsigned long sp)
 {
 	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
-		sp -= get_random_int() & ~PAGE_MASK;
+		sp -= prandom_u32_max(PAGE_SIZE);
 	return sp & ~0xf;
 }

arch/s390/kernel/process.c

@@ -224,7 +224,7 @@ unsigned long __get_wchan(struct task_struct *p)
 unsigned long arch_align_stack(unsigned long sp)
 {
 	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
-		sp -= get_random_int() & ~PAGE_MASK;
+		sp -= prandom_u32_max(PAGE_SIZE);
 	return sp & ~0xf;
 }
 

arch/s390/kernel/vdso.c

@@ -227,7 +227,7 @@ static unsigned long vdso_addr(unsigned long start, unsigned long len)
 	end -= len;
 
 	if (end > start) {
-		offset = get_random_int() % (((end - start) >> PAGE_SHIFT) + 1);
+		offset = prandom_u32_max(((end - start) >> PAGE_SHIFT) + 1);
 		addr = start + (offset << PAGE_SHIFT);
 	} else {
 		addr = start;