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Message-ID: <20190924194139.GA3597785@archlinux-threadripper>
Date: Tue, 24 Sep 2019 12:41:39 -0700
From: Nathan Chancellor <natechancellor@...il.com>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Guenter Roeck <linux@...ck-us.net>,
clang-built-linux <clang-built-linux@...glegroups.com>,
jdelvare@...e.com,
Tomasz Paweł Gajc <tpgxyz@...il.com>,
Henrik Rydberg <rydberg@...math.org>,
linux-hwmon@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] hwmon: (applesmc) fix UB and udelay overflow
On Tue, Sep 24, 2019 at 12:36:44PM -0700, Nick Desaulniers wrote:
> On Tue, Sep 24, 2019 at 11:38 AM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> >
> > On Tue, Sep 24, 2019 at 10:47:28AM -0700, Nick Desaulniers 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@...il.com>
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/678
> > > Debugged-by: Nathan Chancellor <natechancellor@...il.com>
> > > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > > ---
> > > Changes V1 -> V2:
> > > * The first loop in send_byte() needs to break out on the same condition
> > > now. Technically, the loop condition could even be removed. The diff
> > > looks funny because of the duplicated logic between existing and newly
> > > added for loops.
> > >
> > > 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..c76adb504dff 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 */
> > > @@ -190,6 +200,23 @@ static int send_byte(u8 cmd, u16 port)
> > > if (status & 0x04)
> > > return 0;
> > > /* timeout: give up */
> > > + if (us << 1 == APPLESMC_UDELAY_MAX)
> > > + break;
> > > + /* busy: long wait and resend */
> > > + 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;
> > > /* busy: long wait and resend */
> > > --
> > > 2.23.0.351.gc4317032e6-goog
> > >
> >
> > This resolves the __bad_udelay appearance at -O3 for me. I am not
> > familiar enough with this code to give a reviewed by though!
>
> Does that constitute a Tested-by tag?
Given that this could have real implications for the hardware, I would
think tested by would imply running this on said hardware. FWIW:
Build-tested-by: Nathan Chancellor <natechancellor@...il.com>
> >
> > Also, for some odd reason, I couldn't apply your patch with 'git apply':
> >
> > % curl -LSs https://lore.kernel.org/lkml/20190924174728.201464-1-ndesaulniers@google.com/raw | git apply
> > error: corrupt patch at line 117
> >
> > It looks like some of the '=' got changed into =3D and some spaces got
> > changed into =20. Weird encoding glitch?
>
> The text in my email client shows no encoding error; the link above
> shows the issue. Attaching a copy here, in case git-send-email
> related.
Yes, appears git send-email related because your attached patch applies
just fine.
Cheers,
Nathan
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