linux-kernel - Re: [PATCH] random: vDSO: Redefine PAGE_SIZE and PAGE

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Message-ID: <Zs2RCfMgfNu_2vos@zx2c4.com>
Date: Tue, 27 Aug 2024 10:40:41 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Theodore Ts'o <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
	Andy Lutomirski <luto@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH] random: vDSO: Redefine PAGE_SIZE and PAGE_MASK

I don't love this, but it might be the lesser of evils, so sure, let's
do it.

I think I'll combine these header fixups so that the whole operation is
a bit more clear. The commit is still pretty small. Something like
below:

>From 0d9a3d68cd6222395a605abd0ac625c41d4cabfa Mon Sep 17 00:00:00 2001
From: Christophe Leroy <christophe.leroy@...roup.eu>
Date: Tue, 27 Aug 2024 09:31:47 +0200
Subject: [PATCH] random: vDSO: clean header inclusion in getrandom

Depending on the architecture, building a 32-bit vDSO on a 64-bit kernel
is problematic when some system headers are included.

Minimise the amount of headers by moving needed items, such as
__{get,put}_unaligned_t, into dedicated common headers and in general
use more specific headers, similar to what was done in commit
8165b57bca21 ("linux/const.h: Extract common header for vDSO") and
commit 8c59ab839f52 ("lib/vdso: Enable common headers").

On some architectures this results in missing PAGE_SIZE, as was
described by commit 8b3843ae3634 ("vdso/datapage: Quick fix - use
asm/page-def.h for ARM64"), so define this if necessary, in the same way
as done prior by commit cffaefd15a8f ("vdso: Use CONFIG_PAGE_SHIFT in
vdso/datapage.h").

Removing linux/time64.h leads to missing 'struct timespec64' in
x86's asm/pvclock.h. Add a forward declaration of that struct in
that file.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 arch/x86/include/asm/pvclock.h  |  1 +
 include/asm-generic/unaligned.h | 11 +----------
 include/vdso/helpers.h          |  1 +
 include/vdso/unaligned.h        | 15 +++++++++++++++
 lib/vdso/getrandom.c            | 13 ++++++++-----
 5 files changed, 26 insertions(+), 15 deletions(-)
 create mode 100644 include/vdso/unaligned.h

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 0c92db84469d..6e4f8fae3ce9 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -5,6 +5,7 @@
 #include <asm/clocksource.h>
 #include <asm/pvclock-abi.h>

+struct timespec64;
 /* some helper functions for xen and kvm pv clock sources */
 u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src);
 u64 pvclock_clocksource_read_nowd(struct pvclock_vcpu_time_info *src);
diff --git a/include/asm-generic/unaligned.h b/include/asm-generic/unaligned.h
index a84c64e5f11e..95acdd70b3b2 100644
--- a/include/asm-generic/unaligned.h
+++ b/include/asm-generic/unaligned.h
@@ -8,16 +8,7 @@
  */
 #include <linux/unaligned/packed_struct.h>
 #include <asm/byteorder.h>
-
-#define __get_unaligned_t(type, ptr) ({						\
-	const struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);	\
-	__pptr->x;								\
-})
-
-#define __put_unaligned_t(type, val, ptr) do {					\
-	struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);		\
-	__pptr->x = (val);							\
-} while (0)
+#include <vdso/unaligned.h>

 #define get_unaligned(ptr)	__get_unaligned_t(typeof(*(ptr)), (ptr))
 #define put_unaligned(val, ptr) __put_unaligned_t(typeof(*(ptr)), (val), (ptr))
diff --git a/include/vdso/helpers.h b/include/vdso/helpers.h
index 73501149439d..3ddb03bb05cb 100644
--- a/include/vdso/helpers.h
+++ b/include/vdso/helpers.h
@@ -4,6 +4,7 @@

 #ifndef __ASSEMBLY__

+#include <asm/barrier.h>
 #include <vdso/datapage.h>

 static __always_inline u32 vdso_read_begin(const struct vdso_data *vd)
diff --git a/include/vdso/unaligned.h b/include/vdso/unaligned.h
new file mode 100644
index 000000000000..eee3d2a4dbe4
--- /dev/null
+++ b/include/vdso/unaligned.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __VDSO_UNALIGNED_H
+#define __VDSO_UNALIGNED_H
+
+#define __get_unaligned_t(type, ptr) ({						\
+	const struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);	\
+	__pptr->x;								\
+})
+
+#define __put_unaligned_t(type, val, ptr) do {					\
+	struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);		\
+	__pptr->x = (val);							\
+} while (0)
+
+#endif /* __VDSO_UNALIGNED_H */
diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
index 1281fa3546c2..938ca539aaa6 100644
--- a/lib/vdso/getrandom.c
+++ b/lib/vdso/getrandom.c
@@ -4,15 +4,18 @@
  */

 #include <linux/array_size.h>
-#include <linux/cache.h>
-#include <linux/kernel.h>
-#include <linux/time64.h>
+#include <linux/minmax.h>
 #include <vdso/datapage.h>
 #include <vdso/getrandom.h>
+#include <vdso/unaligned.h>
 #include <asm/vdso/getrandom.h>
-#include <asm/vdso/vsyscall.h>
-#include <asm/unaligned.h>
 #include <uapi/linux/mman.h>
+#include <uapi/linux/random.h>
+
+#undef PAGE_SIZE
+#undef PAGE_MASK
+#define PAGE_SIZE (1UL << CONFIG_PAGE_SHIFT)
+#define PAGE_MASK (~(PAGE_SIZE - 1))

 #define MEMCPY_AND_ZERO_SRC(type, dst, src, len) do {				\
 	while (len >= sizeof(type)) {						\
--
2.46.0