[PATCH] perf/x86/intel/uncore: Prefer struct_size over open coded arithmetic

[Erick Archer <erick.archer@outlook.com>]

This is an effort to get rid of all multiplications from allocation
functions in order to prevent integer overflows [1][2].

As the "box" variable is a pointer to "struct intel_uncore_box" and
this structure ends in a flexible array:

struct intel_uncore_box {
	[...]
	struct intel_uncore_extra_reg shared_regs[];
};

the preferred way in the kernel is to use the struct_size() helper to
do the arithmetic instead of the calculation "size + count * size" in
the kzalloc_node() function.

This way, the code is more readable and safer.

This code was detected with the help of Coccinelle, and audited and
modified manually.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
Link: https://github.com/KSPP/linux/issues/160 [2]
Signed-off-by: Erick Archer <erick.archer@outlook.com>
---
Hi,

The Coccinelle script used to detect this code pattern is the following:

virtual report

@rule1@
type t1;
type t2;
identifier i0;
identifier i1;
identifier i2;
identifier ALLOC =~ "kmalloc|kzalloc|kmalloc_node|kzalloc_node|vmalloc|vzalloc|kvmalloc|kvzalloc";
position p1;
@@

i0 = sizeof(t1) + sizeof(t2) * i1;
...
i2 = ALLOC@p1(..., i0, ...);

@script:python depends on report@
p1 << rule1.p1;
@@

msg = "WARNING: verify allocation on line %s" % (p1[0].line)
coccilib.report.print_report(p1[0],msg)

Regards,
Erick
---
 arch/x86/events/intel/uncore.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c
index 258e2cdf28fa..ce756d24c370 100644
--- a/arch/x86/events/intel/uncore.c
+++ b/arch/x86/events/intel/uncore.c
@@ -350,12 +350,11 @@ static void uncore_pmu_init_hrtimer(struct intel_uncore_box *box)
 static struct intel_uncore_box *uncore_alloc_box(struct intel_uncore_type *type,
 						 int node)
 {
-	int i, size, numshared = type->num_shared_regs ;
+	int i, numshared = type->num_shared_regs;
 	struct intel_uncore_box *box;
 
-	size = sizeof(*box) + numshared * sizeof(struct intel_uncore_extra_reg);
-
-	box = kzalloc_node(size, GFP_KERNEL, node);
+	box = kzalloc_node(struct_size(box, shared_regs, numshared), GFP_KERNEL,
+			   node);
 	if (!box)
 		return NULL;
 
-- 
2.25.1