On Wed, May 06, 2020 at 11:24:48PM +0000, Luis Chamberlain wrote:
> On Wed, May 06, 2020 at 06:28:15PM -0400, Rafael Aquini wrote:
> > Analogously to the introduction of panic_on_warn, this patch
> > introduces a kernel option named panic_on_taint in order to
> > provide a simple and generic way to stop execution and catch
> > a coredump when the kernel gets tainted by any given taint flag.
> >
> > This is useful for debugging sessions as it avoids rebuilding
> > the kernel to explicitly add calls to panic() or BUG() into
> > code sites that introduce the taint flags of interest.
> > Another, perhaps less frequent, use for this option would be
> > as a mean for assuring a security policy (in paranoid mode)
> > case where no single taint is allowed for the running system.
> >
> > Suggested-by: Qian Cai <cai@xxxxxx>
> > Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx>
> > ---
> > Documentation/admin-guide/kdump/kdump.rst | 10 ++++++
> > .../admin-guide/kernel-parameters.txt | 3 ++
> > Documentation/admin-guide/sysctl/kernel.rst | 36 +++++++++++++++++++
> > include/linux/kernel.h | 1 +
> > kernel/panic.c | 7 ++++
> > kernel/sysctl.c | 7 ++++
> > 6 files changed, 64 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> > index ac7e131d2935..de3cf6d377cc 100644
> > --- a/Documentation/admin-guide/kdump/kdump.rst
> > +++ b/Documentation/admin-guide/kdump/kdump.rst
> > @@ -521,6 +521,16 @@ will cause a kdump to occur at the panic() call. In cases where a user wants
> > to specify this during runtime, /proc/sys/kernel/panic_on_warn can be set to 1
> > to achieve the same behaviour.
> >
> > +Trigger Kdump on add_taint()
> > +============================
> > +
> > +The kernel parameter, panic_on_taint, calls panic() from within add_taint(),
> > +whenever the value set in this bitmask matches with the bit flag being set
> > +by add_taint(). This will cause a kdump to occur at the panic() call.
> > +In cases where a user wants to specify this during runtime,
> > +/proc/sys/kernel/panic_on_taint can be set to a respective bitmask value
> > +to achieve the same behaviour.
> > +
> > Contact
> > =======
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 7bc83f3d9bdf..75c02c1841b2 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -3404,6 +3404,9 @@
> > panic_on_warn panic() instead of WARN(). Useful to cause kdump
> > on a WARN().
> >
> > + panic_on_taint panic() when the kernel gets tainted, if the taint
> > + flag being set matches with the assigned bitmask.
> > +
> > crash_kexec_post_notifiers
> > Run kdump after running panic-notifiers and dumping
> > kmsg. This only for the users who doubt kdump always
> > diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> > index 0d427fd10941..5b880102f2e3 100644
> > --- a/Documentation/admin-guide/sysctl/kernel.rst
> > +++ b/Documentation/admin-guide/sysctl/kernel.rst
> > @@ -658,6 +658,42 @@ a kernel rebuild when attempting to kdump at the location of a WARN().
> > = ================================================
> >
> >
> > +panic_on_taint
> > +==============
> > +
> > +Bitmask for calling panic() in the add_taint() path.
> > +This is useful to avoid a kernel rebuild when attempting to
> > +kdump at the insertion of any specific TAINT flags.
> > +When set to 0 (default) add_taint() default behavior is maintained.
> > +
> > +====== ============================
> > +bit 0 TAINT_PROPRIETARY_MODULE
> > +bit 1 TAINT_FORCED_MODULE
> > +bit 2 TAINT_CPU_OUT_OF_SPEC
> > +bit 3 TAINT_FORCED_RMMOD
> > +bit 4 TAINT_MACHINE_CHECK
> > +bit 5 TAINT_BAD_PAGE
> > +bit 6 TAINT_USER
> > +bit 7 TAINT_DIE
> > +bit 8 TAINT_OVERRIDDEN_ACPI_TABLE
> > +bit 9 TAINT_WARN
> > +bit 10 TAINT_CRAP
> > +bit 11 TAINT_FIRMWARE_WORKAROUND
> > +bit 12 TAINT_OOT_MODULE
> > +bit 13 TAINT_UNSIGNED_MODULE
> > +bit 14 TAINT_SOFTLOCKUP
> > +bit 15 TAINT_LIVEPATCH
> > +bit 16 TAINT_AUX
> > +bit 17 TAINT_RANDSTRUCT
> > +bit 18 TAINT_FLAGS_COUNT
> > +====== ============================
> > +
> > +So, for example, to panic if the kernel gets tainted due to
> > +occurrences of bad pages and/or machine check errors, a user can::
> > +
> > + echo 48 > /proc/sys/kernel/panic_on_taint
> > +
> > +
> > panic_print
> > ===========
> >
> > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > index 9b7a8d74a9d6..518b9fd381c2 100644
> > --- a/include/linux/kernel.h
> > +++ b/include/linux/kernel.h
> > @@ -528,6 +528,7 @@ extern int panic_on_oops;
> > extern int panic_on_unrecovered_nmi;
> > extern int panic_on_io_nmi;
> > extern int panic_on_warn;
> > +extern unsigned long panic_on_taint;
> > extern int sysctl_panic_on_rcu_stall;
> > extern int sysctl_panic_on_stackoverflow;
> >
> > diff --git a/kernel/panic.c b/kernel/panic.c
> > index b69ee9e76cb2..e2d4771ab911 100644
> > --- a/kernel/panic.c
> > +++ b/kernel/panic.c
> > @@ -44,6 +44,7 @@ static int pause_on_oops_flag;
> > static DEFINE_SPINLOCK(pause_on_oops_lock);
> > bool crash_kexec_post_notifiers;
> > int panic_on_warn __read_mostly;
> > +unsigned long panic_on_taint __read_mostly;
>
> What justification do we have for using __read_mostly here?
> See patch I just sent out, hope that helps.
>
Given the rationale on the hint usage (from your re-sent patch)
this one should not be hinted. I'll get rid of the hint.
> > int panic_timeout = CONFIG_PANIC_TIMEOUT;
> > EXPORT_SYMBOL_GPL(panic_timeout);
> > @@ -434,6 +435,11 @@ void add_taint(unsigned flag, enum lockdep_ok lockdep_ok)
> > pr_warn("Disabling lock debugging due to kernel taint\n");
> >
> > set_bit(flag, &tainted_mask);
> > +
> > + if (unlikely(tainted_mask & panic_on_taint)) {
>
> unlikely() is telling the merit may not be that strong?
>
> > + panic_on_taint = 0;
> > + panic("panic_on_taint set ...");
> > + }
> > }
> > EXPORT_SYMBOL(add_taint);
> >
> > @@ -675,6 +681,7 @@ core_param(panic, panic_timeout, int, 0644);
> > core_param(panic_print, panic_print, ulong, 0644);
> > core_param(pause_on_oops, pause_on_oops, int, 0644);
> > core_param(panic_on_warn, panic_on_warn, int, 0644);
> > +core_param(panic_on_taint, panic_on_taint, ulong, 0644);
> > core_param(crash_kexec_post_notifiers, crash_kexec_post_notifiers, bool, 0644);
> >
> > static int __init oops_setup(char *s)
> > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > index 8a176d8727a3..b80ab660d727 100644
> > --- a/kernel/sysctl.c
> > +++ b/kernel/sysctl.c
> > @@ -1217,6 +1217,13 @@ static struct ctl_table kern_table[] = {
> > .extra1 = SYSCTL_ZERO,
> > .extra2 = SYSCTL_ONE,
> > },
> > + {
> > + .procname = "panic_on_taint",
> > + .data = &panic_on_taint,
> > + .maxlen = sizeof(unsigned long),
> > + .mode = 0644,
> > + .proc_handler = proc_doulongvec_minmax,
>
> proc_doulongvec_minmax supports a min and max, do we want to
> set it so that we have a sanity check for values used? To see
> an example, refer to the file-max entry.
>
It didn't seem necessary to declare the range limits here, as
albeit he current set of taint flags would cause tainted_mask
to strecth all the way from 0 (none set) to ULONG_MAX (all set),
that's its valid range given the usage.
That's why I didn't declare the extra values for range-checking.
I can do it, though, if you rather have it that way.
> That would allow for example to error our if a value was
> tried but it is a taint flag which we don't support on an older
> kernel.
>
> You know what would be *really* useful as well, is a way to
> cat out our current taint, and perhaps another that spits it
> out in English. This can allow scripts to check that for
> validity, instead of scraping kernel logs.
>
> For instance, I would love to easily just check if TAIN_WARN
> was hit on some tests I am working on, but I don't want to scrape
> the kernel log for this, as I think this is overkill.
>
I can definitely take a look into these suggestions for a later
patch, as I think they're nice but they don't look as a deal-breaker
for the simple feature being proposed here.
Thanks for your feedback!
-- Rafael
