Re: [PATCH] kprobes: Enable tracing for mololithic kernel images

From: Jarkko Sakkinen <jarkko@kernel.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: "Luis Chamberlain" <mcgrof@kernel.org>,
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Subject: Re: [PATCH] kprobes: Enable tracing for mololithic kernel images
Date: Thu, 16 Jun 2022 00:24:04 +0300	[thread overview]
Message-ID: <YqpN9NAkAKhgiunQ@iki.fi> (raw)
In-Reply-To: <144b7e90-5d75-7e2c-4e54-8a73f914dfdf@csgroup.eu>

On Tue, Jun 14, 2022 at 12:36:25PM +0000, Christophe Leroy wrote:
> 
> 
> Le 14/06/2022 à 14:26, Jarkko Sakkinen a écrit :
> > On Thu, Jun 09, 2022 at 06:44:45AM -0700, Luis Chamberlain wrote:
> >> On Thu, Jun 09, 2022 at 08:47:38AM +0100, Russell King (Oracle) wrote:
> >>> On Wed, Jun 08, 2022 at 02:59:27AM +0300, Jarkko Sakkinen wrote:
> >>>> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> >>>> index 553866751e1a..d2bb954cd54f 100644
> >>>> --- a/arch/arm/kernel/Makefile
> >>>> +++ b/arch/arm/kernel/Makefile
> >>>> @@ -44,6 +44,11 @@ obj-$(CONFIG_CPU_IDLE)		+= cpuidle.o
> >>>>   obj-$(CONFIG_ISA_DMA_API)	+= dma.o
> >>>>   obj-$(CONFIG_FIQ)		+= fiq.o fiqasm.o
> >>>>   obj-$(CONFIG_MODULES)		+= armksyms.o module.o
> >>>> +ifeq ($(CONFIG_MODULES),y)
> >>>> +obj-y				+= module_alloc.o
> >>>> +else
> >>>> +obj-$(CONFIG_KPROBES)		+= module_alloc.o
> >>>> +endif
> >>>
> >>> Doesn't:
> >>>
> >>> obj-$(CONFIG_MODULES)		+= module_alloc.o
> >>> obj-$(CONFIG_KPROBES)		+= module_alloc.o
> >>
> >> That just begs for a new kconfig symbol for the object, and for
> >> the object then to be built with it.
> >>
> >> The archs which override the default can use ARCH_HAS_VM_ALLOC_EXEC.
> >> Please note that the respective free is important as well and its
> >> not clear if we need an another define for the free. Someone has
> >> to do that work. We want to ensure to noexec the code on free and
> >> this can vary on each arch.
> > 
> > Let me check if I understand this (not 100% sure).
> > 
> > So if arch define ARCH_HAS_VMALLOC_EXEC, then this would set
> > config flag CONFIG_VMALLOC_EXEC, which would be used to include
> > the compilation unit?
> > 
> 
> I guess you have two possible approaches.
> 
> Either architectures select CONFIG_ARCH_HAS_VMALLOC_EXEC at all time and 
> then you add a CONFIG_VMALLOC_EXEC which depends on 
> CONFIG_ARCH_HAS_VMALLOC_EXEC and CONFIG_MODULES or CONFIG_KPROBES,
> 
> Or architectures select CONFIG_ARCH_HAS_VMALLOC_EXEC only when either 
> CONFIG_MODULES or CONFIG_KPROBES is selected, in that case there is no 
> need for a CONFIG_VMALLOC_EXEC.

Right, got it now. Thanks for the elaboration.

> Christophe

BR, Jarkko