linux-kernel - RE: [PATCH] ACPICA: fix UBSAN warning using __builtin

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Date:   Mon, 8 Jun 2020 23:20:43 +0000
From:   "Kaneda, Erik" <erik.kaneda@...el.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
CC:     "Moore, Robert" <robert.moore@...el.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        Len Brown <lenb@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "glider@...gle.com" <glider@...gle.com>,
        "guohanjun@...wei.com" <guohanjun@...wei.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "pcc@...gle.com" <pcc@...gle.com>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "will@...nel.org" <will@...nel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "devel@...ica.org" <devel@...ica.org>
Subject: RE: [PATCH] ACPICA: fix UBSAN warning using __builtin_offsetof



> -----Original Message-----
> From: Nick Desaulniers <ndesaulniers@...gle.com>
> Sent: Tuesday, June 2, 2020 11:47 AM
> To: Kaneda, Erik <erik.kaneda@...el.com>
> Cc: Moore, Robert <robert.moore@...el.com>; Wysocki, Rafael J
> <rafael.j.wysocki@...el.com>; Len Brown <lenb@...nel.org>; Ard
> Biesheuvel <ardb@...nel.org>; dvyukov@...gle.com; glider@...gle.com;
> guohanjun@...wei.com; linux-arm-kernel@...ts.infradead.org; linux-
> kernel@...r.kernel.org; lorenzo.pieralisi@....com;
> mark.rutland@....com; pcc@...gle.com; rjw@...ysocki.net;
> will@...nel.org; stable@...r.kernel.org; linux-acpi@...r.kernel.org;
> devel@...ica.org
> Subject: Re: [PATCH] ACPICA: fix UBSAN warning using __builtin_offsetof
> 
> On Mon, Jun 1, 2020 at 5:03 PM Kaneda, Erik <erik.kaneda@...el.com>
> wrote:
> >
> >
> > Hi,
> >
> > > Will reported UBSAN warnings:
> > > UBSAN: null-ptr-deref in drivers/acpi/acpica/tbfadt.c:459:37
> > > UBSAN: null-ptr-deref in arch/arm64/kernel/smp.c:596:6
> > >
> > > Looks like the emulated offsetof macro ACPI_OFFSET is causing these.
> > > We can avoid this by using the compiler builtin, __builtin_offsetof.
> >
> > I'll take a look at this tomorrow
> > >
> > > The non-kernel runtime of UBSAN would print:
> > > runtime error: member access within null pointer of type for this macro.
> >
> > actypes.h is owned by ACPICA so we typically do not allow
> > compiler-specific extensions because the code is intended to be
> > compiled using the C99 standard without compiler extensions. We could
> > allow this sort of thing in a Linux-specific header file like
> include/acpi/platform/aclinux.h but I'll take a look at the error as well..
> 
Hi,

> If I'm not allowed to touch that header, it looks like I can include
> <linux/stddef.h> (rather than my host's <stddef.h>) to get a definition of

Why not use your host's stddef.h?

> `offsetof` thats implemented in terms of `__builtin_offsetof`.  I should be
> able to use that to replace uses of ACPI_OFFSET.  Are any of these off limits?

Yes, the idea is to define ACPI_OFFSET in a way that you want so that we don't touch the uses below.

Erik
> 
> $ grep -rn ACPI_OFFSET
> arch/arm64/include/asm/acpi.h:34:#define
> ACPI_MADT_GICC_MIN_LENGTH
> ACPI_OFFSET(  \ arch/arm64/include/asm/acpi.h:41:#define
> ACPI_MADT_GICC_SPE (ACPI_OFFSET(struct acpi_madt_generic_interrupt, \
> include/acpi/actbl.h:376:#define ACPI_FADT_OFFSET(f)             (u16)
> ACPI_OFFSET (struct acpi_table_fadt, f)
> drivers/acpi/acpica/acresrc.h:84:#define ACPI_RS_OFFSET(f)
>   (u8) ACPI_OFFSET (struct acpi_resource,f)
> drivers/acpi/acpica/acresrc.h:85:#define AML_OFFSET(f)
>   (u8) ACPI_OFFSET (union aml_resource,f)
> drivers/acpi/acpica/acinterp.h:17:#define ACPI_EXD_OFFSET(f)
> (u8) ACPI_OFFSET (union acpi_operand_object,f)
> drivers/acpi/acpica/acinterp.h:18:#define ACPI_EXD_NSOFFSET(f)
> (u8) ACPI_OFFSET (struct acpi_namespace_node,f)
> drivers/acpi/acpica/rsdumpinfo.c:16:#define ACPI_RSD_OFFSET(f)
>  (u8) ACPI_OFFSET (union acpi_resource_data,f)
> drivers/acpi/acpica/rsdumpinfo.c:17:#define ACPI_PRT_OFFSET(f)
>  (u8) ACPI_OFFSET (struct acpi_pci_routing_table,f)
> 
> --
> Thanks,
> ~Nick Desaulniers