* [PATCH] mdio-mux-gpio: Remove VLA usage
@ 2018-05-29 22:59 Kees Cook
2018-05-29 23:19 ` Joe Perches
2018-05-30 0:57 ` Andrew Lunn
0 siblings, 2 replies; 3+ messages in thread
From: Kees Cook @ 2018-05-29 22:59 UTC (permalink / raw)
To: Linus Walleij
Cc: Pramod Kumar, Andrew Lunn, Florian Fainelli, David S. Miller,
linux-gpio, linux-kernel
In the quest to remove all stack VLA usage from the kernel[1], this
allocates the values buffer during the callback instead of putting it
on the stack.
[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/net/phy/mdio-mux-gpio.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/net/phy/mdio-mux-gpio.c b/drivers/net/phy/mdio-mux-gpio.c
index 082ffef0dec4..e99994f4ed50 100644
--- a/drivers/net/phy/mdio-mux-gpio.c
+++ b/drivers/net/phy/mdio-mux-gpio.c
@@ -26,18 +26,23 @@ static int mdio_mux_gpio_switch_fn(int current_child, int desired_child,
void *data)
{
struct mdio_mux_gpio_state *s = data;
- int values[s->gpios->ndescs];
+ int *values;
unsigned int n;
if (current_child == desired_child)
return 0;
+ values = kmalloc_array(s->gpios->ndescs, sizeof(*values), GFP_KERNEL);
+ if (!values)
+ return -ENOMEM;
+
for (n = 0; n < s->gpios->ndescs; n++)
values[n] = (desired_child >> n) & 1;
gpiod_set_array_value_cansleep(s->gpios->ndescs, s->gpios->desc,
values);
+ kfree(values);
return 0;
}
--
2.17.0
--
Kees Cook
Pixel Security
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] mdio-mux-gpio: Remove VLA usage
2018-05-29 22:59 [PATCH] mdio-mux-gpio: Remove VLA usage Kees Cook
@ 2018-05-29 23:19 ` Joe Perches
2018-05-30 0:57 ` Andrew Lunn
1 sibling, 0 replies; 3+ messages in thread
From: Joe Perches @ 2018-05-29 23:19 UTC (permalink / raw)
To: Kees Cook, Linus Walleij
Cc: Pramod Kumar, Andrew Lunn, Florian Fainelli, David S. Miller,
linux-gpio, linux-kernel
On Tue, 2018-05-29 at 15:59 -0700, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> allocates the values buffer during the callback instead of putting it
> on the stack.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
[]
> diff --git a/drivers/net/phy/mdio-mux-gpio.c b/drivers/net/phy/mdio-mux-gpio.c
[]
> @@ -26,18 +26,23 @@ static int mdio_mux_gpio_switch_fn(int current_child, int desired_child,
> void *data)
> {
> struct mdio_mux_gpio_state *s = data;
> - int values[s->gpios->ndescs];
> + int *values;
> unsigned int n;
>
> if (current_child == desired_child)
> return 0;
>
> + values = kmalloc_array(s->gpios->ndescs, sizeof(*values), GFP_KERNEL);
> + if (!values)
> + return -ENOMEM;
This function previously only returned 0
and now it can return -ENOMEM.
How do you know all the indirect callers
via the switch_fn stored in mdio_mux_init
can handle the new return value?
If you have explored these code paths, it
would be good to explain that in the commit
message.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] mdio-mux-gpio: Remove VLA usage
2018-05-29 22:59 [PATCH] mdio-mux-gpio: Remove VLA usage Kees Cook
2018-05-29 23:19 ` Joe Perches
@ 2018-05-30 0:57 ` Andrew Lunn
1 sibling, 0 replies; 3+ messages in thread
From: Andrew Lunn @ 2018-05-30 0:57 UTC (permalink / raw)
To: Kees Cook
Cc: Linus Walleij, Pramod Kumar, Florian Fainelli, David S. Miller,
linux-gpio, linux-kernel
On Tue, May 29, 2018 at 03:59:01PM -0700, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> allocates the values buffer during the callback instead of putting it
> on the stack.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> drivers/net/phy/mdio-mux-gpio.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/phy/mdio-mux-gpio.c b/drivers/net/phy/mdio-mux-gpio.c
> index 082ffef0dec4..e99994f4ed50 100644
> --- a/drivers/net/phy/mdio-mux-gpio.c
> +++ b/drivers/net/phy/mdio-mux-gpio.c
> @@ -26,18 +26,23 @@ static int mdio_mux_gpio_switch_fn(int current_child, int desired_child,
> void *data)
> {
> struct mdio_mux_gpio_state *s = data;
> - int values[s->gpios->ndescs];
> + int *values;
> unsigned int n;
>
> if (current_child == desired_child)
> return 0;
>
> + values = kmalloc_array(s->gpios->ndescs, sizeof(*values), GFP_KERNEL);
> + if (!values)
> + return -ENOMEM;
> +
> for (n = 0; n < s->gpios->ndescs; n++)
> values[n] = (desired_child >> n) & 1;
>
> gpiod_set_array_value_cansleep(s->gpios->ndescs, s->gpios->desc,
> values);
>
> + kfree(values);
> return 0;
> }
Hi Kees
This is the 'hot path' for this driver, and you are making it more
expensive.
Please allocate the memory once in mdio_mux_gpio_probe and make it
part of mdio_mux_gpio_state.
Thanks
Andrew
^ permalink raw reply [flat|nested] 3+ messages in thread
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2018-05-29 22:59 [PATCH] mdio-mux-gpio: Remove VLA usage Kees Cook
2018-05-29 23:19 ` Joe Perches
2018-05-30 0:57 ` Andrew Lunn
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