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Message-ID: <8390ac81-7774-4e67-9739-c2b98813d6da@csgroup.eu>
Date: Mon, 2 Sep 2024 15:19:56 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: "Jason A. Donenfeld" <Jason@...c4.com>,
Adhemerval Zanella Netto <adhemerval.zanella@...aro.org>
Cc: Will Deacon <will@...nel.org>, Theodore Ts'o <tytso@....edu>,
linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
Catalin Marinas <catalin.marinas@....com>,
Thomas Gleixner <tglx@...utronix.de>, Eric Biggers <ebiggers@...nel.org>,
ardb@...nel.org
Subject: Re: [PATCH v2] aarch64: vdso: Wire up getrandom() vDSO implementation
Le 02/09/2024 à 15:11, Jason A. Donenfeld a écrit :
> Hey Christophe (for header logic) & Will (for arm64 stuff),
>
> On Fri, Aug 30, 2024 at 09:28:29AM -0300, Adhemerval Zanella Netto wrote:
>>>> diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
>>>> index 938ca539aaa6..7c9711248d9b 100644
>>>> --- a/lib/vdso/getrandom.c
>>>> +++ b/lib/vdso/getrandom.c
>>>> @@ -5,6 +5,7 @@
>>>>
>>>> #include <linux/array_size.h>
>>>> #include <linux/minmax.h>
>>>> +#include <linux/mm.h>
>>>> #include <vdso/datapage.h>
>>>> #include <vdso/getrandom.h>
>>>> #include <vdso/unaligned.h>
>>>
>>> Looks like this should be a separate change?
>>
>>
>> It is required so arm64 can use c-getrandom-y, otherwise vgetrandom.o build
>> fails:
>>
>> CC arch/arm64/kernel/vdso/vgetrandom.o
>> In file included from ./include/uapi/linux/mman.h:5,
>> from /mnt/projects/linux/linux-git/lib/vdso/getrandom.c:13,
>> from <command-line>:
>> ./arch/arm64/include/asm/mman.h: In function ‘arch_calc_vm_prot_bits’:
>> ./arch/arm64/include/asm/mman.h:14:13: error: implicit declaration of function ‘system_supports_bti’ [-Werror=implicit-function-declaration]
>> 14 | if (system_supports_bti() && (prot & PROT_BTI))
>> | ^~~~~~~~~~~~~~~~~~~
>> ./arch/arm64/include/asm/mman.h:15:24: error: ‘VM_ARM64_BTI’ undeclared (first use in this function); did you mean ‘ARM64_BTI’?
>> 15 | ret |= VM_ARM64_BTI;
>> | ^~~~~~~~~~~~
>> | ARM64_BTI
>> ./arch/arm64/include/asm/mman.h:15:24: note: each undeclared identifier is reported only once for each function it appears in
>> ./arch/arm64/include/asm/mman.h:17:13: error: implicit declaration of function ‘system_supports_mte’ [-Werror=implicit-function-declaration]
>> 17 | if (system_supports_mte() && (prot & PROT_MTE))
>> | ^~~~~~~~~~~~~~~~~~~
>> ./arch/arm64/include/asm/mman.h:18:24: error: ‘VM_MTE’ undeclared (first use in this function)
>> 18 | ret |= VM_MTE;
>> | ^~~~~~
>> ./arch/arm64/include/asm/mman.h: In function ‘arch_calc_vm_flag_bits’:
>> ./arch/arm64/include/asm/mman.h:32:24: error: ‘VM_MTE_ALLOWED’ undeclared (first use in this function)
>> 32 | return VM_MTE_ALLOWED;
>> | ^~~~~~~~~~~~~~
>> ./arch/arm64/include/asm/mman.h: In function ‘arch_validate_flags’:
>> ./arch/arm64/include/asm/mman.h:59:29: error: ‘VM_MTE’ undeclared (first use in this function)
>> 59 | return !(vm_flags & VM_MTE) || (vm_flags & VM_MTE_ALLOWED);
>> | ^~~~~~
>> ./arch/arm64/include/asm/mman.h:59:52: error: ‘VM_MTE_ALLOWED’ undeclared (first use in this function)
>> 59 | return !(vm_flags & VM_MTE) || (vm_flags & VM_MTE_ALLOWED);
>> | ^~~~~~~~~~~~~~
>> arch/arm64/kernel/vdso/vgetrandom.c: In function ‘__kernel_getrandom’:
>> arch/arm64/kernel/vdso/vgetrandom.c:18:25: error: ‘ENOSYS’ undeclared (first use in this function); did you mean ‘ENOSPC’?
>> 18 | return -ENOSYS;
>> | ^~~~~~
>> | ENOSPC
>> cc1: some warnings being treated as errors
>>
>> I can move to a different patch, but this is really tied to this patch.
>
> Adhemerval kept this change in this patch for v3, which, if it's
> necessary, is fine with me. But I was looking to see if there was
> another way of doing it, because including linux/mm.h inside of vdso
> code is kind of contrary to your project with e379299fe0b3 ("random:
> vDSO: minimize and simplify header includes").
>
> getrandom.c includes uapi/linux/mman.h for the mmap constants. That
> seems fine; it's userspace code after all. But then uapi/linux/mman.h
> has this:
>
> #include <asm/mman.h>
> #include <asm-generic/hugetlb_encode.h>
> #include <linux/types.h>
>
> The asm-generic/ one resolves to uapi/asm-generic. But the asm/ one
> resolves to arch code, which is where we then get in trouble on ARM,
> where arch/arm64/include/asm/mman.h has all sorts of kernel code in it.
>
> Maybe, instead, it should resolve to arch/arm64/include/uapi/asm/mman.h,
> which is the header that userspace actually uses in normal user code?
>
> Is this a makefile problem? What's going on here? Seems like this is
> something worth sorting out. Or I can take Adhemerval's v3 as-is and
> we'll grit our teeth and work it out later, as you prefer. But I thought
> I should mention it.
That's a tricky problem, I also have it on powerpc, see patch 5, I
solved it that way:
In the Makefile:
-ccflags-y := -fno-common -fno-builtin
+ccflags-y := -fno-common -fno-builtin -DBUILD_VDSO
In arch/powerpc/include/asm/mman.h:
diff --git a/arch/powerpc/include/asm/mman.h
b/arch/powerpc/include/asm/mman.h
index 17a77d47ed6d..42a51a993d94 100644
--- a/arch/powerpc/include/asm/mman.h
+++ b/arch/powerpc/include/asm/mman.h
@@ -6,7 +6,7 @@
#include <uapi/asm/mman.h>
-#ifdef CONFIG_PPC64
+#if defined(CONFIG_PPC64) && !defined(BUILD_VDSO)
#include <asm/cputable.h>
#include <linux/mm.h>
So that the only thing that remains in arch/powerpc/include/asm/mman.h
when building a VDSO is #include <uapi/asm/mman.h>
I got the idea from ARM64, they use something similar in their
arch/arm64/include/asm/rwonce.h
Christophe
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