On Wed, Sep 29, 2021 at 10:01:33PM +0300, Alexander Popov wrote: > On 29.09.2021 21:58, Alexander Popov wrote: > > Currently, the Linux kernel provides two types of reaction to kernel > > warnings: > > 1. Do nothing (by default), > > 2. Call panic() if panic_on_warn is set. That's a very strong reaction, > > so panic_on_warn is usually disabled on production systems. > > > > From a safety point of view, the Linux kernel misses a middle way of > > handling kernel warnings: > > - The kernel should stop the activity that provokes a warning, > > - But the kernel should avoid complete denial of service. > > > > From a security point of view, kernel warning messages provide a lot of > > useful information for attackers. Many GNU/Linux distributions allow > > unprivileged users to read the kernel log, so attackers use kernel > > warning infoleak in vulnerability exploits. See the examples: > > https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html > > https://a13xp0p0v.github.io/2021/02/09/CVE-2021-26708.html > > > > Let's introduce the pkill_on_warn boot parameter. > > If this parameter is set, the kernel kills all threads in a process > > that provoked a kernel warning. This behavior is reasonable from a safety > > point of view described above. It is also useful for kernel security > > hardening because the system kills an exploit process that hits a > > kernel warning. > > > > Signed-off-by: Alexander Popov <alex.popov@xxxxxxxxx> > > This patch was tested using CONFIG_LKDTM. > The kernel kills a process that performs this: > echo WARNING > /sys/kernel/debug/provoke-crash/DIRECT > > If you are fine with this approach, I will prepare a patch adding the > pkill_on_warn sysctl. I suspect that you need a list of kthreads for which you are better off just invoking panic(). RCU's various kthreads, for but one set of examples. Thanx, Paul > Best regards, > Alexander > > > --- > > Documentation/admin-guide/kernel-parameters.txt | 4 ++++ > > kernel/panic.c | 5 +++++ > > 2 files changed, 9 insertions(+) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > index 91ba391f9b32..86c748907666 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -4112,6 +4112,10 @@ > > pirq= [SMP,APIC] Manual mp-table setup > > See Documentation/x86/i386/IO-APIC.rst. > > > > + pkill_on_warn= Kill all threads in a process that provoked a > > + kernel warning. > > + Format: { "0" | "1" } > > + > > plip= [PPT,NET] Parallel port network link > > Format: { parport<nr> | timid | 0 } > > See also Documentation/admin-guide/parport.rst. > > diff --git a/kernel/panic.c b/kernel/panic.c > > index cefd7d82366f..47b728bfb1d3 100644 > > --- a/kernel/panic.c > > +++ b/kernel/panic.c > > @@ -53,6 +53,7 @@ static int pause_on_oops_flag; > > static DEFINE_SPINLOCK(pause_on_oops_lock); > > bool crash_kexec_post_notifiers; > > int panic_on_warn __read_mostly; > > +int pkill_on_warn __read_mostly; > > unsigned long panic_on_taint; > > bool panic_on_taint_nousertaint = false; > > > > @@ -610,6 +611,9 @@ void __warn(const char *file, int line, void *caller, unsigned taint, > > > > print_oops_end_marker(); > > > > + if (pkill_on_warn && system_state >= SYSTEM_RUNNING) > > + do_group_exit(SIGKILL); > > + > > /* Just a warning, don't kill lockdep. */ > > add_taint(taint, LOCKDEP_STILL_OK); > > } > > @@ -694,6 +698,7 @@ 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(pkill_on_warn, pkill_on_warn, int, 0644); > > core_param(crash_kexec_post_notifiers, crash_kexec_post_notifiers, bool, 0644); > > > > static int __init oops_setup(char *s) > > >
