From db38d5c106dfdd7cb7207c83267d82fdf4950b61 Mon Sep 17 00:00:00 2001 From: Rafael Aquini Date: Sun, 7 Jun 2020 21:40:17 -0700 Subject: [PATCH] kernel: add panic_on_taint 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 flag. This is useful for debugging sessions as it avoids having to rebuild the kernel to explicitly add calls to panic() into the code sites that introduce the taint flags of interest. For instance, if one is interested in proceeding with a post-mortem analysis at the point a given code path is hitting a bad page (i.e. unaccount_page_cache_page(), or slab_bug()), a coredump can be collected by rebooting the kernel with 'panic_on_taint=0x20' amended to the command line. Another, perhaps less frequent, use for this option would be as a means for assuring a security policy case where only a subset of taints, or no single taint (in paranoid mode), is allowed for the running system. The optional switch 'nousertaint' is handy in this particular scenario, as it will avoid userspace induced crashes by writes to sysctl interface /proc/sys/kernel/tainted causing false positive hits for such policies. [akpm@linux-foundation.org: tweak kernel-parameters.txt wording] Suggested-by: Qian Cai Signed-off-by: Rafael Aquini Signed-off-by: Andrew Morton Reviewed-by: Luis Chamberlain Cc: Dave Young Cc: Baoquan He Cc: Jonathan Corbet Cc: Kees Cook Cc: Randy Dunlap Cc: "Theodore Ts'o" Cc: Adrian Bunk Cc: Greg Kroah-Hartman Cc: Laura Abbott Cc: Jeff Mahoney Cc: Jiri Kosina Cc: Takashi Iwai Link: http://lkml.kernel.org/r/20200515175502.146720-1-aquini@redhat.com Signed-off-by: Linus Torvalds --- Documentation/admin-guide/kdump/kdump.rst | 8 +++++ .../admin-guide/kernel-parameters.txt | 13 +++++++ Documentation/admin-guide/sysctl/kernel.rst | 7 ++++ include/linux/kernel.h | 3 ++ kernel/panic.c | 34 +++++++++++++++++++ kernel/sysctl.c | 11 +++++- 6 files changed, 75 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst index ac7e131d2935..2da65fef2a1c 100644 --- a/Documentation/admin-guide/kdump/kdump.rst +++ b/Documentation/admin-guide/kdump/kdump.rst @@ -521,6 +521,14 @@ 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 facilitates a conditional call to 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 add_taint()->panic() call. + Contact ======= diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index f3eeecbb3f63..df9b0fe2ed60 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3447,6 +3447,19 @@ bit 4: print ftrace buffer bit 5: print all printk messages in buffer + panic_on_taint= Bitmask for conditionally calling panic() in add_taint() + Format: [,nousertaint] + Hexadecimal bitmask representing the set of TAINT flags + that will cause the kernel to panic when add_taint() is + called with any of the flags in this set. + The optional switch "nousertaint" can be utilized to + prevent userspace forced crashes by writing to sysctl + /proc/sys/kernel/tainted any flagset matching with the + bitmask set on panic_on_taint. + See Documentation/admin-guide/tainted-kernels.rst for + extra details on the taint flags that users can pick + to compose the bitmask to assign to panic_on_taint. + panic_on_warn panic() instead of WARN(). Useful to cause kdump on a WARN(). diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst index 1ebf68d01141..3b00b9223157 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -1239,6 +1239,13 @@ ORed together. The letters are seen in "Tainted" line of Oops reports. See :doc:`/admin-guide/tainted-kernels` for more information. +Note: + writes to this sysctl interface will fail with ``EINVAL`` if the kernel is + booted with the command line option ``panic_on_taint=,nousertaint`` + and any of the ORed together values being written to ``tainted`` match with + the bitmask declared on panic_on_taint. + See :doc:`/admin-guide/kernel-parameters` for more details on that particular + kernel command line option and its optional ``nousertaint`` switch. threads-max =========== diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 9b7a8d74a9d6..f7835db7102e 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -528,6 +528,8 @@ 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 bool panic_on_taint_nousertaint; extern int sysctl_panic_on_rcu_stall; extern int sysctl_panic_on_stackoverflow; @@ -596,6 +598,7 @@ extern enum system_states { #define TAINT_AUX 16 #define TAINT_RANDSTRUCT 17 #define TAINT_FLAGS_COUNT 18 +#define TAINT_FLAGS_MAX ((1UL << TAINT_FLAGS_COUNT) - 1) struct taint_flag { char c_true; /* character printed when tainted */ diff --git a/kernel/panic.c b/kernel/panic.c index b69ee9e76cb2..94b5c973770c 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -44,6 +44,8 @@ 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; +bool panic_on_taint_nousertaint = false; int panic_timeout = CONFIG_PANIC_TIMEOUT; EXPORT_SYMBOL_GPL(panic_timeout); @@ -434,6 +436,11 @@ 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 (tainted_mask & panic_on_taint) { + panic_on_taint = 0; + panic("panic_on_taint set ..."); + } } EXPORT_SYMBOL(add_taint); @@ -686,3 +693,30 @@ static int __init oops_setup(char *s) return 0; } early_param("oops", oops_setup); + +static int __init panic_on_taint_setup(char *s) +{ + char *taint_str; + + if (!s) + return -EINVAL; + + taint_str = strsep(&s, ","); + if (kstrtoul(taint_str, 16, &panic_on_taint)) + return -EINVAL; + + /* make sure panic_on_taint doesn't hold out-of-range TAINT flags */ + panic_on_taint &= TAINT_FLAGS_MAX; + + if (!panic_on_taint) + return -EINVAL; + + if (s && !strcmp(s, "nousertaint")) + panic_on_taint_nousertaint = true; + + pr_info("panic_on_taint: bitmask=0x%lx nousertaint_mode=%sabled\n", + panic_on_taint, panic_on_taint_nousertaint ? "en" : "dis"); + + return 0; +} +early_param("panic_on_taint", panic_on_taint_setup); diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 715774d8c55f..587ed0494f2f 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -866,11 +866,20 @@ static int proc_taint(struct ctl_table *table, int write, return err; if (write) { + int i; + + /* + * If we are relying on panic_on_taint not producing + * false positives due to userspace input, bail out + * before setting the requested taint flags. + */ + if (panic_on_taint_nousertaint && (tmptaint & panic_on_taint)) + return -EINVAL; + /* * Poor man's atomic or. Not worth adding a primitive * to everyone's atomic.h for this */ - int i; for (i = 0; i < BITS_PER_LONG && tmptaint >> i; i++) { if ((tmptaint >> i) & 1) add_taint(i, LOCKDEP_STILL_OK); -- 2.20.1