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

[Jessica Yu]

+++ 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@xxxxxxxxxx
>
> 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@xxxxxxxx>
> ---
> 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