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Date: Thu, 08 Sep 2016 05:59:25 +0930
From: Rusty Russell <rusty@...tcorp.com.au>
To: Petr Mladek <pmladek@...e.com>
Cc: 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,
Petr Mladek <pmladek@...e.com>, Jessica Yu <jeyu@...hat.com>
Subject: Re: [PATCH] module/taint: Automatically increase the buffer size for new taint flags
Petr Mladek <pmladek@...e.com> writes:
> 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().
I agree, nice work!
Minor nitpick: the winged ' /* 0 */' comments imply the values matter,
but they don't. I'd skip that.
I've CC'd Jessica to add to her review pile :)
Thanks,
Rusty.
> 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! */
> +};
> +
> +extern const char *print_tainted(void);
> +extern void add_taint(enum taint_flags flag, enum lockdep_ok);
> +extern int test_taint(enum taint_flags flag);
> +extern unsigned long get_taint(void);
>
> extern const char hex_asc[];
> #define hex_asc_lo(x) hex_asc[((x) & 0x0f)]
> diff --git a/kernel/module.c b/kernel/module.c
> index 529efae9f481..fb6c0d425b47 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -4036,6 +4036,10 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
> }
> #endif /* CONFIG_KALLSYMS */
>
> +/* Maximum number of characters written by module_flags() */
> +#define MODULE_FLAGS_BUF_SIZE (TAINT_FLAGS_COUNT + 4)
> +
> +/* Keep in sync with MODULE_FLAGS_BUF_SIZE !!! */
> static char *module_flags(struct module *mod, char *buf)
> {
> int bx = 0;
> @@ -4080,7 +4084,7 @@ static void m_stop(struct seq_file *m, void *p)
> static int m_show(struct seq_file *m, void *p)
> {
> struct module *mod = list_entry(p, struct module, list);
> - char buf[8];
> + char buf[MODULE_FLAGS_BUF_SIZE];
>
> /* We always ignore unformed modules. */
> if (mod->state == MODULE_STATE_UNFORMED)
> @@ -4251,7 +4255,7 @@ EXPORT_SYMBOL_GPL(__module_text_address);
> void print_modules(void)
> {
> struct module *mod;
> - char buf[8];
> + char buf[MODULE_FLAGS_BUF_SIZE];
>
> printk(KERN_DEFAULT "Modules linked in:");
> /* Most callers should already have preempt disabled, but make sure */
> diff --git a/kernel/panic.c b/kernel/panic.c
> index ca8cea1ef673..e90125bf9238 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -334,7 +334,7 @@ const char *print_tainted(void)
> return buf;
> }
>
> -int test_taint(unsigned flag)
> +int test_taint(enum taint_flags flag)
> {
> return test_bit(flag, &tainted_mask);
> }
> @@ -353,7 +353,7 @@ unsigned long get_taint(void)
> * If something bad has gone wrong, you'll want @lockdebug_ok = false, but for
> * some notewortht-but-not-corrupting cases, it can be set to true.
> */
> -void add_taint(unsigned flag, enum lockdep_ok lockdep_ok)
> +void add_taint(enum taint_flags flag, enum lockdep_ok lockdep_ok)
> {
> if (lockdep_ok == LOCKDEP_NOW_UNRELIABLE && __debug_locks_off())
> pr_warn("Disabling lock debugging due to kernel taint\n");
> --
> 1.8.5.6
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