2024-05-11 14:52:27

by Erick Archer

Subject: [PATCH] perf/x86/amd/uncore: Add flex array to struct amd_uncore_ctx

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

The "struct amd_uncore_ctx" can be refactored to use a flex array for
the "events" member. This way, the allocation/freeing of the memory can
be simplified.

Specifically, as the "curr" variable is a pointer to the amd_uncore_ctx
structure and it now ends up in a flexible array:

struct amd_uncore_ctx {
[...]
struct perf_event *events[];
};

the two-step allocation can be simplifief by using just one kzalloc_node
function and the struct_size() helper to do the arithmetic calculation
for the memory to be allocated.

This way, the code is more readable and safer.

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]
Suggested-by: Christophe JAILLET <[email protected]>
Signed-off-by: Erick Archer <[email protected]>
---
Hi,

This patch can be considered v4 of this other one [1]. However, since
the patch has completely changed due to the addition of the flex array,
I have decided to make a new series and remove the "Reviewed-by:" tag
by Gustavo A. R. Silva and Kees cook.

[1] https://lore.kernel.org/linux-hardening/PAXPR02MB7248F46DEFA47E79677481B18B152@PAXPR02MB7248.eurprd02.prod.outlook.com/

Thanks,
Erick
---
arch/x86/events/amd/uncore.c | 18 +++++-------------
1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
index 4ccb8fa483e6..86755d16a3b2 100644
--- a/arch/x86/events/amd/uncore.c
+++ b/arch/x86/events/amd/uncore.c
@@ -37,8 +37,8 @@ static int pmu_version;
struct amd_uncore_ctx {
int refcnt;
int cpu;
- struct perf_event **events;
struct hlist_node node;
+ struct perf_event *events[];
};

struct amd_uncore_pmu {
@@ -426,10 +426,8 @@ static void amd_uncore_ctx_free(struct amd_uncore *uncore, unsigned int cpu)
if (cpu == ctx->cpu)
cpumask_clear_cpu(cpu, &pmu->active_mask);

- if (!--ctx->refcnt) {
- kfree(ctx->events);
+ if (!--ctx->refcnt)
kfree(ctx);
- }

*per_cpu_ptr(pmu->ctx, cpu) = NULL;
}
@@ -474,19 +472,13 @@ static int amd_uncore_ctx_init(struct amd_uncore *uncore, unsigned int cpu)
/* Allocate context if sibling does not exist */
if (!curr) {
node = cpu_to_node(cpu);
- curr = kzalloc_node(sizeof(*curr), GFP_KERNEL, node);
+ curr = kzalloc_node(struct_size(curr, events,
+ pmu->num_counters),
+ GFP_KERNEL, node);
if (!curr)
goto fail;

curr->cpu = cpu;
- curr->events = kzalloc_node(sizeof(*curr->events) *
- pmu->num_counters,
- GFP_KERNEL, node);
- if (!curr->events) {
- kfree(curr);
- goto fail;
- }
-
cpumask_set_cpu(cpu, &pmu->active_mask);
}

--
2.25.1

2024-05-11 20:05:03

by Kees Cook

Subject: Re: [PATCH] perf/x86/amd/uncore: Add flex array to struct amd_uncore_ctx

On Sat, May 11, 2024 at 04:51:54PM +0200, Erick Archer wrote:
> This is an effort to get rid of all multiplications from allocation
> functions in order to prevent integer overflows [1][2].
>
> The "struct amd_uncore_ctx" can be refactored to use a flex array for
> the "events" member. This way, the allocation/freeing of the memory can
> be simplified.
>
> Specifically, as the "curr" variable is a pointer to the amd_uncore_ctx
> structure and it now ends up in a flexible array:
>
> struct amd_uncore_ctx {
> [...]
> struct perf_event *events[];
> };
>
> the two-step allocation can be simplifief by using just one kzalloc_node
> function and the struct_size() helper to do the arithmetic calculation
> for the memory to be allocated.
>
> This way, the code is more readable and safer.
>
> 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]
> Suggested-by: Christophe JAILLET <[email protected]>
> Signed-off-by: Erick Archer <[email protected]>
> ---
> Hi,
>
> This patch can be considered v4 of this other one [1]. However, since
> the patch has completely changed due to the addition of the flex array,
> I have decided to make a new series and remove the "Reviewed-by:" tag
> by Gustavo A. R. Silva and Kees cook.
>
> [1] https://lore.kernel.org/linux-hardening/PAXPR02MB7248F46DEFA47E79677481B18B152@PAXPR02MB7248.eurprd02.prod.outlook.com/
>
> Thanks,
> Erick
> ---
> arch/x86/events/amd/uncore.c | 18 +++++-------------
> 1 file changed, 5 insertions(+), 13 deletions(-)

My favorite kind of patch: fewer lines, clearer code.

Reviewed-by: Kees Cook <[email protected]>

-Kees

--
Kees Cook