Re: [PATCH for-4.20 v2] ARM32/traps: Fix do_trap_undefined_instruction()'s detection of kernel text

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 2/11/25 1:54 PM, Andrew Cooper wrote:

> While fixing some common/arch boundaries for UBSAN support on other
> architectures, the following debugging patch:
>
>   diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
>   index c1f2d1b89d43..58d1d048d339 100644
>   --- a/xen/arch/arm/setup.c
>   +++ b/xen/arch/arm/setup.c
>   @@ -504,6 +504,8 @@ void asmlinkage __init start_xen(unsigned long fdt_paddr)
>
>        system_state = SYS_STATE_active;
>
>   +    dump_execution_state();
>   +
>        for_each_domain( d )
>            domain_unpause_by_systemcontroller(d);
>
> failed with:
>
>   (XEN) *** Serial input to DOM0 (type 'CTRL-a' three times to switch input)
>   (XEN) CPU0: Unexpected Trap: Undefined Instruction
>   (XEN) ----[ Xen-4.20-rc  arm32  debug=n  Not tainted ]----
>   (XEN) CPU:    0
>   <snip>
>   (XEN)
>   (XEN) ****************************************
>   (XEN) Panic on CPU 0:
>   (XEN) CPU0: Unexpected Trap: Undefined Instruction
>   (XEN) ****************************************
>
> This is because the condition for init text is wrong.  While there's nothing
> interesting from that point onwards in start_xen(), it's also wrong for
> livepatches too.
>
> Use is_active_kernel_text() which is the correct test for this purpose, and is
> aware of init and livepatch regions as well as their lifetimes.
>
> Fixes: 3e802c6ca1fb ("xen/arm: Correctly support WARN_ON")
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>     
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

~ Oleksii
> ---
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien@xxxxxxx>
> CC: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
> CC: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> CC: Michal Orzel <michal.orzel@xxxxxxx>
> CC: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
>
> v2:
>  * Split out change to dump_execution_state()
>
> Sample run going wrong:
>   https://gitlab.com/xen-project/people/andyhhp/xen/-/jobs/9078570105
>
> Sample run with dump_execution_state() working:
>   https://gitlab.com/xen-project/people/andyhhp/xen/-/jobs/9079185111
> ---
>  xen/arch/arm/arm32/traps.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/xen/arch/arm/arm32/traps.c b/xen/arch/arm/arm32/traps.c
> index a2fc1c22cbc9..b88d41811b49 100644
> --- a/xen/arch/arm/arm32/traps.c
> +++ b/xen/arch/arm/arm32/traps.c
> @@ -36,8 +36,7 @@ void do_trap_undefined_instruction(struct cpu_user_regs *regs)
>      uint32_t pc = regs->pc;
>      uint32_t instr;
>  
> -    if ( !is_kernel_text(pc) &&
> -         (system_state >= SYS_STATE_active || !is_kernel_inittext(pc)) )
> +    if ( !is_active_kernel_text(pc) )
>          goto die;
>  
>      /* PC should be always a multiple of 4, as Xen is using ARM instruction set */
>