From: Nick Desaulniers <ndesaulniers@google.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: clang-built-linux <clang-built-linux@googlegroups.com>,
jdelvare@suse.com, "Tomasz Paweł Gajc" <tpgxyz@gmail.com>,
"Nathan Chancellor" <natechancellor@gmail.com>,
"Henrik Rydberg" <rydberg@bitmath.org>,
linux-hwmon@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] hwmon: (applesmc) fix UB and udelay overflow
Date: Tue, 24 Sep 2019 10:42:16 -0700 [thread overview]
Message-ID: <CAKwvOd=GVdHhsdHOMpuhEKkWMssW37keqX5c59+6fiEgLs+Q1g@mail.gmail.com> (raw)
In-Reply-To: <20190924173717.198637-1-ndesaulniers@google.com>
On Tue, Sep 24, 2019 at 10:37 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> Fixes the following 2 issues in the driver:
> 1. Left shifting a signed integer is undefined behavior. Unsigned
> integral types should be used for bitwise operations.
> 2. The delay scales from 0x0010 to 0x20000 by powers of 2, but udelay
> will result in a linkage failure when given a constant that's greater
> than 20000 (0x4E20). Agressive loop unrolling can fully unroll the
> loop, resulting in later iterations overflowing the call to udelay.
>
> 2 is fixed via splitting the loop in two, iterating the first up to the
> point where udelay would overflow, then switching to mdelay, as
> suggested in Documentation/timers/timers-howto.rst.
>
> Reported-by: Tomasz Paweł Gajc <tpgxyz@gmail.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/678
> Debugged-by: Nathan Chancellor <natechancellor@gmail.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> drivers/hwmon/applesmc.c | 35 +++++++++++++++++++++++++++++++----
> 1 file changed, 31 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
> index 183ff3d25129..2bc12812f52f 100644
> --- a/drivers/hwmon/applesmc.c
> +++ b/drivers/hwmon/applesmc.c
> @@ -46,6 +46,7 @@
> #define APPLESMC_MIN_WAIT 0x0010
> #define APPLESMC_RETRY_WAIT 0x0100
> #define APPLESMC_MAX_WAIT 0x20000
> +#define APPLESMC_UDELAY_MAX 20000
>
> #define APPLESMC_READ_CMD 0x10
> #define APPLESMC_WRITE_CMD 0x11
> @@ -157,14 +158,23 @@ static struct workqueue_struct *applesmc_led_wq;
> static int wait_read(void)
> {
> u8 status;
> - int us;
> - for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
> + unsigned int us;
> +
> + for (us = APPLESMC_MIN_WAIT; us < APPLESMC_UDELAY_MAX; us <<= 1) {
> udelay(us);
> status = inb(APPLESMC_CMD_PORT);
> /* read: wait for smc to settle */
> if (status & 0x01)
> return 0;
> }
> + /* switch to mdelay for longer sleeps */
> + for (; us < APPLESMC_MAX_WAIT; us <<= 1) {
> + mdelay(us);
> + status = inb(APPLESMC_CMD_PORT);
> + /* read: wait for smc to settle */
> + if (status & 0x01)
> + return 0;
> + }
>
> pr_warn("wait_read() fail: 0x%02x\n", status);
> return -EIO;
> @@ -177,10 +187,10 @@ static int wait_read(void)
> static int send_byte(u8 cmd, u16 port)
> {
> u8 status;
> - int us;
> + unsigned int us;
>
> outb(cmd, port);
> - for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
> + for (us = APPLESMC_MIN_WAIT; us < APPLESMC_UDELAY_MAX; us <<= 1) {
> udelay(us);
> status = inb(APPLESMC_CMD_PORT);
> /* write: wait for smc to settle */
> @@ -196,6 +206,23 @@ static int send_byte(u8 cmd, u16 port)
> udelay(APPLESMC_RETRY_WAIT);
> outb(cmd, port);
> }
> + /* switch to mdelay for longer sleeps */
> + for (; us < APPLESMC_MAX_WAIT; us <<= 1) {
> + mdelay(us);
> + status = inb(APPLESMC_CMD_PORT);
> + /* write: wait for smc to settle */
> + if (status & 0x02)
> + continue;
> + /* ready: cmd accepted, return */
> + if (status & 0x04)
> + return 0;
> + /* timeout: give up */
> + if (us << 1 == APPLESMC_MAX_WAIT)
> + break;
Sorry, I need to modify the first for loop in this function to break
out properly. v2 inbound.
> + /* busy: long wait and resend */
> + udelay(APPLESMC_RETRY_WAIT);
> + outb(cmd, port);
> + }
>
> pr_warn("send_byte(0x%02x, 0x%04x) fail: 0x%02x\n", cmd, port, status);
> return -EIO;
> --
> 2.23.0.351.gc4317032e6-goog
>
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2019-09-24 17:42 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-24 17:37 [PATCH] hwmon: (applesmc) fix UB and udelay overflow Nick Desaulniers
2019-09-24 17:42 ` Nick Desaulniers [this message]
2019-09-24 17:47 ` [PATCH v2] " Nick Desaulniers
2019-09-24 18:38 ` Nathan Chancellor
2019-09-24 19:36 ` Nick Desaulniers
2019-09-24 19:41 ` Nathan Chancellor
2019-09-30 21:46 ` Cengiz Can
2019-10-01 0:01 ` Guenter Roeck
2019-10-02 21:43 ` Nick Desaulniers
2019-10-03 1:17 ` Guenter Roeck
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