Re: [PATCH v2] x86/dumpstack: Fix misleading instruction pointer error message

[Oleg Nesterov]

On 11/16, Thomas Gleixner wrote:
>
> Subject: x86/dumpstack: Don't try to access user space code of other tasks
> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Date: Mon, 16 Nov 2020 22:26:52 +0100
> 
> sysrq-t ends up invoking show_opcodes() for each task which tries to access
> the user space code of other processes which is obviously bogus.
> 
> It either manages to dump where the foreign tasks regs->ip points to in
> currents mapping or triggers a pagefault and prints "Code: Bad RIP
> value.". Both is just wrong.
> 
> Add a safeguard in copy_code() and check whether the @regs pointer matches
> currents pt_regs. If not, do not even try to access it.
> 
> While at it, add commentry why using copy_from_user_nmi() is safe in
> copy_code() even if the function name suggests otherwise.
> 
> Reported-by: Mark Mossberg <mark.mossberg@xxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>