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Date: Mon, 27 Jan 2020 15:51:37 +0300
From: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To: Grzegorz Halat <ghalat@...hat.com>, linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
linux-doc@...r.kernel.org, ssaner@...hat.com, atomlin@...hat.com,
oleksandr@...hat.com, vbendel@...hat.com, kirill@...temov.name,
borntraeger@...ibm.com, Andrew Morton <akpm@...ux-foundation.org>,
Iurii Zaikin <yzaikin@...gle.com>,
Kees Cook <keescook@...omium.org>,
Luis Chamberlain <mcgrof@...nel.org>,
Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH 1/1] mm: sysctl: add panic_on_mm_error sysctl
On 27/01/2020 13.11, Grzegorz Halat wrote:
> Memory management subsystem performs various checks at runtime,
> if an inconsistency is detected then such event is being logged and kernel
> continues to run. While debugging such problems it is helpful to collect
> memory dump as early as possible. Currently, there is no easy way to panic
> kernel when such error is detected.
>
> It was proposed[1] to panic the kernel if panic_on_oops is set but this
> approach was not accepted. One of alternative proposals was introduction of
> a new sysctl.
>
> The patch adds panic_on_mm_error sysctl. If the sysctl is set then the
> kernel will be crashed when an inconsistency is detected by memory
> management. This currently means panic when bad page or bad PTE
> is detected(this may be extended to other places in MM).
>
> Another use case of this sysctl may be in security-wise environments,
> it may be more desired to crash machine than continue to run with
> potentially damaged data structures.
>
> [1] https://marc.info/?l=linux-mm&m=142649500728327&w=2
>
> Signed-off-by: Grzegorz Halat <ghalat@...hat.com>
> ---
> Documentation/admin-guide/sysctl/kernel.rst | 12 ++++++++++++
> include/linux/kernel.h | 1 +
> kernel/sysctl.c | 9 +++++++++
> mm/memory.c | 7 +++++++
> mm/page_alloc.c | 4 +++-
> 5 files changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index def074807cee..2fecd6b2547e 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -61,6 +61,7 @@ show up in /proc/sys/kernel:
> - overflowgid
> - overflowuid
> - panic
> +- panic_on_mm_error
> - panic_on_oops
> - panic_on_stackoverflow
> - panic_on_unrecovered_nmi
> @@ -611,6 +612,17 @@ an IO error.
> and you can use this option to take a crash dump.
>
>
> +panic_on_mm_error:
> +==============
> +
> +Controls the kernel's behaviour when inconsistency is detected
> +by memory management code, for example bad page state or bad PTE.
> +
> +0: try to continue operation.
> +
> +1: panic immediately.
> +
> +
> panic_on_oops:
> ==============
>
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 0d9db2a14f44..5f9d408512ff 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -518,6 +518,7 @@ extern int oops_in_progress; /* If set, an oops, panic(), BUG() or die() is in
> extern int panic_timeout;
> extern unsigned long panic_print;
> extern int panic_on_oops;
> +extern int panic_on_mm_error;
> extern int panic_on_unrecovered_nmi;
> extern int panic_on_io_nmi;
> extern int panic_on_warn;
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 70665934d53e..6477e1cce28b 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1238,6 +1238,15 @@ static struct ctl_table kern_table[] = {
> .extra1 = SYSCTL_ZERO,
> .extra2 = SYSCTL_ONE,
> },
> + {
> + .procname = "panic_on_mm_error",
> + .data = &panic_on_mm_error,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = SYSCTL_ZERO,
> + .extra2 = SYSCTL_ONE,
> + },
> #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
> {
> .procname = "timer_migration",
> diff --git a/mm/memory.c b/mm/memory.c
> index 45442d9a4f52..cce74ff39447 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -71,6 +71,7 @@
> #include <linux/dax.h>
> #include <linux/oom.h>
> #include <linux/numa.h>
> +#include <linux/module.h>
>
> #include <trace/events/kmem.h>
>
> @@ -88,6 +89,8 @@
> #warning Unfortunate NUMA and NUMA Balancing config, growing page-frame for last_cpupid.
> #endif
>
> +int panic_on_mm_error __read_mostly;
> +
> #ifndef CONFIG_NEED_MULTIPLE_NODES
> /* use the per-pgdat data instead for discontigmem - mbligh */
> unsigned long max_mapnr;
> @@ -543,6 +546,10 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
> vma->vm_ops ? vma->vm_ops->fault : NULL,
> vma->vm_file ? vma->vm_file->f_op->mmap : NULL,
> mapping ? mapping->a_ops->readpage : NULL);
> +
> + print_modules();
I'm not sure that printing all modules for each bad pte is a good idea.
It already prints 'readpage' which is enough to guess filesystem or driver.
Maybe print modules under if (panic...) below?
> + if (panic_on_mm_error)
> + panic("Bad page map detected");
> dump_stack();
> add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> }
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d047bf7d8fd4..2ea6a65ba011 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -643,9 +643,11 @@ static void bad_page(struct page *page, const char *reason,
> if (bad_flags)
> pr_alert("bad because of flags: %#lx(%pGp)\n",
> bad_flags, &bad_flags);
> - dump_page_owner(page);
>
> + dump_page_owner(page);
> print_modules();
> + if (panic_on_mm_error)
> + panic("Bad page state detected");
> dump_stack();
> out:
> /* Leave bad fields for debug, except PageBuddy could make trouble */
>
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