linux-kernel - Re: module/taint: Automatically increase the buffer size for new taint flags

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Message-ID: <20160908010006.GA26819@packer-debian-8-amd64.digitalocean.com>
Date:   Wed, 7 Sep 2016 21:00:07 -0400
From:   Jessica Yu <jeyu@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Rusty Russell <rusty@...tcorp.com.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: module/taint: Automatically increase the buffer size for new
 taint flags

+++ Petr Mladek [07/09/16 15:13 +0200]:
>The commit 66cc69e34e86a231 ("Fix: module signature vs tracepoints:
>add new TAINT_UNSIGNED_MODULE") updated module_taint_flags() to
>potentially print one more character. But it did not increase the
>size of the corresponding buffers in m_show() and print_modules().
>
>We have recently done the same mistake when adding a taint flag
>for livepatching, see
>https://lkml.kernel.org/g/cfba2c823bb984690b73572aaae1db596b54a082.1472137475.git.jpoimboe@redhat.com
>
>Let's convert the taint flags into enum and handle the buffer size
>almost automatically.
>
>It is not optimal because only few taint flags can be printed by
>module_taint_flags(). But better be on the safe side. IMHO, it is
>not worth the optimization and this is a good compromise.
>
>Signed-off-by: Petr Mladek <pmladek@...e.com>
>---
> include/linux/kernel.h | 44 ++++++++++++++++++++++++--------------------
> kernel/module.c        |  8 ++++++--
> kernel/panic.c         |  4 ++--
> 3 files changed, 32 insertions(+), 24 deletions(-)
>
>diff --git a/include/linux/kernel.h b/include/linux/kernel.h
>index d96a6118d26a..1809bc82b7a5 100644
>--- a/include/linux/kernel.h
>+++ b/include/linux/kernel.h
>@@ -472,14 +472,10 @@ static inline void set_arch_panic_timeout(int timeout, int arch_default_timeout)
> 	if (panic_timeout == arch_default_timeout)
> 		panic_timeout = timeout;
> }
>-extern const char *print_tainted(void);
> enum lockdep_ok {
> 	LOCKDEP_STILL_OK,
> 	LOCKDEP_NOW_UNRELIABLE
> };
>-extern void add_taint(unsigned flag, enum lockdep_ok);
>-extern int test_taint(unsigned flag);
>-extern unsigned long get_taint(void);
> extern int root_mountflags;
>
> extern bool early_boot_irqs_disabled;
>@@ -493,22 +489,30 @@ extern enum system_states {
> 	SYSTEM_RESTART,
> } system_state;
>
>-#define TAINT_PROPRIETARY_MODULE	0
>-#define TAINT_FORCED_MODULE		1
>-#define TAINT_CPU_OUT_OF_SPEC		2
>-#define TAINT_FORCED_RMMOD		3
>-#define TAINT_MACHINE_CHECK		4
>-#define TAINT_BAD_PAGE			5
>-#define TAINT_USER			6
>-#define TAINT_DIE			7
>-#define TAINT_OVERRIDDEN_ACPI_TABLE	8
>-#define TAINT_WARN			9
>-#define TAINT_CRAP			10
>-#define TAINT_FIRMWARE_WORKAROUND	11
>-#define TAINT_OOT_MODULE		12
>-#define TAINT_UNSIGNED_MODULE		13
>-#define TAINT_SOFTLOCKUP		14
>-#define TAINT_LIVEPATCH			15
>+enum taint_flags {
>+	TAINT_PROPRIETARY_MODULE,	/*  0 */
>+	TAINT_FORCED_MODULE,		/*  1 */
>+	TAINT_CPU_OUT_OF_SPEC,		/*  2 */
>+	TAINT_FORCED_RMMOD,		/*  3 */
>+	TAINT_MACHINE_CHECK,		/*  4 */
>+	TAINT_BAD_PAGE,			/*  5 */
>+	TAINT_USER,			/*  6 */
>+	TAINT_DIE,			/*  7 */
>+	TAINT_OVERRIDDEN_ACPI_TABLE,	/*  8 */
>+	TAINT_WARN,			/*  9 */
>+	TAINT_CRAP,			/* 10 */
>+	TAINT_FIRMWARE_WORKAROUND,	/* 11 */
>+	TAINT_OOT_MODULE,		/* 12 */
>+	TAINT_UNSIGNED_MODULE,		/* 13 */
>+	TAINT_SOFTLOCKUP,		/* 14 */
>+	TAINT_LIVEPATCH,		/* 15 */
>+	TAINT_FLAGS_COUNT		/* keep last! */
>+};

I liked the enum idea because we got TAINT_FLAGS_COUNT for free :-)
however I think we need to switch back to the #defines because of the kbuild
error.

The "Error: invalid operands...for `<<'" messages are related to the
__WARN_TAINT() macro (arch/arm64/include/asm/bug.h) which emits some assembly
that relies on the taint values. We don't have access to the enum values
in the assembler so we start getting things like:

        .short ((1 << 0) | ((TAINT_WARN) << 8))

where TAINT_WARN should have already been preprocessed, and this is where that
invalid operand error is coming from.

Jessica