Re: [PATCH v2] aarch64: vdso: Wire up getrandom() vDSO implementation

From: Christophe Leroy
Date: Mon Sep 02 2024 - 09:20:10 EST



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