linux-kernel - [tip: timers/vdso] x86/vdso: Fix latent bug in vclock

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Message-ID: <174012859759.10177.14504433418628527411.tip-bot2@tip-bot2>
Date: Fri, 21 Feb 2025 09:03:17 -0000
From:
 tip-bot2 for Thomas Weißschuh <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: thomas.weissschuh@...utronix.de, Thomas Gleixner <tglx@...utronix.de>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
 [tip: timers/vdso] x86/vdso: Fix latent bug in vclock_pages calculation

The following commit has been merged into the timers/vdso branch of tip:

Commit-ID:     3ef32d90cdaa0cfa6c4ffd18f8d646a658163e3d
Gitweb:        https://git.kernel.org/tip/3ef32d90cdaa0cfa6c4ffd18f8d646a658163e3d
Author:        Thomas Weißschuh <thomas.weissschuh@...utronix.de>
AuthorDate:    Tue, 04 Feb 2025 13:05:33 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Fri, 21 Feb 2025 09:54:00 +01:00

x86/vdso: Fix latent bug in vclock_pages calculation

The vclock pages are *after* the non-vclock pages. Currently there are both
two vclock and two non-vclock pages so the existing logic works by
accident.  As soon as the number of pages changes it will break however.
This will be the case with the introduction of the generic vDSO data
storage.

Use a macro to keep the calculation understandable and in sync between
the linker script and mapping code.

Fixes: e93d2521b27f ("x86/vdso: Split virtual clock pages into dedicated mapping")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/all/20250204-vdso-store-rng-v3-1-13a4669dfc8c@linutronix.de

---
 arch/x86/entry/vdso/vdso-layout.lds.S | 2 +-
 arch/x86/entry/vdso/vma.c             | 2 +-
 arch/x86/include/asm/vdso/vsyscall.h  | 1 +
 3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S
index 872947c..918606f 100644
--- a/arch/x86/entry/vdso/vdso-layout.lds.S
+++ b/arch/x86/entry/vdso/vdso-layout.lds.S
@@ -24,7 +24,7 @@ SECTIONS
 
 	timens_page  = vvar_start + PAGE_SIZE;
 
-	vclock_pages = vvar_start + VDSO_NR_VCLOCK_PAGES * PAGE_SIZE;
+	vclock_pages = VDSO_VCLOCK_PAGES_START(vvar_start);
 	pvclock_page = vclock_pages + VDSO_PAGE_PVCLOCK_OFFSET * PAGE_SIZE;
 	hvclock_page = vclock_pages + VDSO_PAGE_HVCLOCK_OFFSET * PAGE_SIZE;
 
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 39e6efc..aa62949 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -290,7 +290,7 @@ static int map_vdso(const struct vdso_image *image, unsigned long addr)
 	}
 
 	vma = _install_special_mapping(mm,
-				       addr + (__VVAR_PAGES - VDSO_NR_VCLOCK_PAGES) * PAGE_SIZE,
+				       VDSO_VCLOCK_PAGES_START(addr),
 				       VDSO_NR_VCLOCK_PAGES * PAGE_SIZE,
 				       VM_READ|VM_MAYREAD|VM_IO|VM_DONTDUMP|
 				       VM_PFNMAP,
diff --git a/arch/x86/include/asm/vdso/vsyscall.h b/arch/x86/include/asm/vdso/vsyscall.h
index 37b4a70..88b31d4 100644
--- a/arch/x86/include/asm/vdso/vsyscall.h
+++ b/arch/x86/include/asm/vdso/vsyscall.h
@@ -6,6 +6,7 @@
 #define __VVAR_PAGES	4
 
 #define VDSO_NR_VCLOCK_PAGES	2
+#define VDSO_VCLOCK_PAGES_START(_b)	((_b) + (__VVAR_PAGES - VDSO_NR_VCLOCK_PAGES) * PAGE_SIZE)
 #define VDSO_PAGE_PVCLOCK_OFFSET	0
 #define VDSO_PAGE_HVCLOCK_OFFSET	1