Re: [PATCH 2/2] printk/console: Enhance the check for consoles using init memory

[Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>]

On (07/14/17 14:51), Petr Mladek wrote:
> printk_late_init() is responsible for disabling boot consoles that
> use init memory. It checks the address of struct console for this.
> 
> But this is not enough. For example, there are several early
> consoles that have write() method in the init section and
> struct console in the normal section. They are not disabled
> and could cause fancy and hard to debug system states.
> 
> It is even more complicated by the macros EARLYCON_DECLARE() and
> OF_EARLYCON_DECLARE() where various struct members are set at
> runtime by the provided setup() function.
> 
> I have tried to reproduce this problem and forced the classic uart
> early console to stay using keep_bootcon parameter. In particular
> I used earlycon=uart,io,0x3f8 keep_bootcon console=ttyS0,115200.
> The system did not boot:
> 
> [    1.570496] PM: Image not found (code -22)
> [    1.570496] PM: Image not found (code -22)
> [    1.571886] PM: Hibernation image not present or could not be loaded.
> [    1.571886] PM: Hibernation image not present or could not be loaded.
> [    1.576407] Freeing unused kernel memory: 2528K
> [    1.577244] kernel tried to execute NX-protected page - exploit attempt? (uid: 0)
> 
> The double lines are caused by having both early uart console and
> ttyS0 console enabled at the same time. The early console stopped
> working when the init memory was freed. Fortunately, the invalid
> call was caught by the NX-protexted page check and did not cause
> any silent fancy problems.
> 
> This patch adds a check for many other addresses stored in
> struct console. It omits setup() and match() that are used
> only when the console is registered. Therefore they have
> already been used at this point and there is no reason
> to use them again.
> 
> Signed-off-by: Petr Mladek <pmladek@suse.com>

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

	-ss