linux-kernel - [PATCH 2/4] random: vDSO: Don't use PAGE_SIZE and PAGE

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Message-ID: <b8f8fb6d1d10386c74f2d8826b737a74c60b76b2.1724743492.git.christophe.leroy@csgroup.eu>
Date: Tue, 27 Aug 2024 09:31:48 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: "Theodore Ts'o" <tytso@....edu>,
	"Jason A. Donenfeld" <Jason@...c4.com>,
	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>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	linux-arch@...r.kernel.org
Subject: [PATCH 2/4] random: vDSO: Don't use PAGE_SIZE and PAGE_MASK

Using PAGE_SIZE and PAGE_MASK in VDSO requires inclusion of
page.h and it creates several problems, see
commit 8b3843ae3634 ("vdso/datapage: Quick fix - use asm/page-def.h
for ARM64") and commit cffaefd15a8f ("vdso: Use CONFIG_PAGE_SHIFT in
vdso/datapage.h").

An easy solution would be to define PAGE_SIZE and PAGE_MASK in vDSO
when they do not exist already, but this can be misleading.

So follow the same approach as commit cffaefd15a8f ("vdso: Use
CONFIG_PAGE_SHIFT in vdso/datapage.h") and exclusively use
CONFIG_PAGE_SHIFT. To avoid too much ugliness, define local consts
that constains the calculated page size and page mask.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
v3: Use local consts instead of _PAGE_SIZE and _PAGE_MASK macros that are already defined by some architectures.
---
 lib/vdso/getrandom.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
index f1643656d0b0..5874e3072bfe 100644
--- a/lib/vdso/getrandom.c
+++ b/lib/vdso/getrandom.c
@@ -65,7 +65,9 @@ static __always_inline ssize_t
 __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_t len,
 		       unsigned int flags, void *opaque_state, size_t opaque_len)
 {
-	ssize_t ret = min_t(size_t, INT_MAX & PAGE_MASK /* = MAX_RW_COUNT */, len);
+	const unsigned long page_size = 1UL << CONFIG_PAGE_SHIFT;
+	const unsigned long page_mask = ~(page_size - 1);
+	ssize_t ret = min_t(size_t, INT_MAX & page_mask /* = MAX_RW_COUNT */, len);
 	struct vgetrandom_state *state = opaque_state;
 	size_t batch_len, nblocks, orig_len = len;
 	bool in_use, have_retried = false;
@@ -84,7 +86,7 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_
 	}
 
 	/* The state must not straddle a page, since pages can be zeroed at any time. */
-	if (unlikely(((unsigned long)opaque_state & ~PAGE_MASK) + sizeof(*state) > PAGE_SIZE))
+	if (unlikely(((unsigned long)opaque_state & ~page_mask) + sizeof(*state) > page_size))
 		return -EFAULT;
 
 	/* Handle unexpected flags by falling back to the kernel. */
-- 
2.44.0