From: Anton Blanchard <anton@ozlabs.org>
To: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
miltonm@us.ibm.com
Cc: linuxppc-dev@lists.ozlabs.org
Subject: [PATCH] powerpc/vdso: Fix vdso cpu truncation
Date: Thu, 16 Jul 2020 09:37:04 +1000 [thread overview]
Message-ID: <20200715233704.1352257-1-anton@ozlabs.org> (raw)
From: Milton Miller <miltonm@us.ibm.com>
The code in vdso_cpu_init that exposes the cpu and numa node to
userspace via SPRG_VDSO incorrctly masks the cpu to 12 bits. This means
that any kernel running on a box with more than 4096 threads (NR_CPUS
advertises a limit of of 8192 cpus) would expose userspace to two cpu
contexts running at the same time with the same cpu number.
Note: I'm not aware of any distro shipping a kernel with support for more
than 4096 threads today, nor of any system image that currently exceeds
4096 threads. Found via code browsing.
Fixes: 18ad51dd342a7eb09dbcd059d0b451b616d4dafc ("powerpc: Add VDSO version of getcpu")
Signed-off-by: Milton Miller <miltonm@us.ibm.com>
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
---
arch/powerpc/kernel/vdso.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index e0f4ba45b6cc..8dad44262e75 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -677,7 +677,7 @@ int vdso_getcpu_init(void)
node = cpu_to_node(cpu);
WARN_ON_ONCE(node > 0xffff);
- val = (cpu & 0xfff) | ((node & 0xffff) << 16);
+ val = (cpu & 0xffff) | ((node & 0xffff) << 16);
mtspr(SPRN_SPRG_VDSO_WRITE, val);
get_paca()->sprg_vdso = val;
--
2.26.2
next reply other threads:[~2020-07-15 23:39 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-15 23:37 Anton Blanchard [this message]
2020-07-16 12:55 ` [PATCH] powerpc/vdso: Fix vdso cpu truncation Michael Ellerman
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