Commit 2bd7aaf1 authored by Milton Miller's avatar Milton Miller Committed by Kelsey Skunberg

powerpc/vdso: Fix vdso cpu truncation

BugLink: https://bugs.launchpad.net/bugs/1892822

[ Upstream commit a9f675f9 ]

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: 18ad51dd ("powerpc: Add VDSO version of getcpu")
Signed-off-by: default avatarMilton Miller <miltonm@us.ibm.com>
Signed-off-by: default avatarAnton Blanchard <anton@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200715233704.1352257-1-anton@ozlabs.orgSigned-off-by: default avatarSasha Levin <sashal@kernel.org>
Signed-off-by: default avatarKhalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: default avatarIan May <ian.may@canonical.com>
Signed-off-by: default avatarKelsey Skunberg <kelsey.skunberg@canonical.com>
parent 2f864fcf
...@@ -702,7 +702,7 @@ int vdso_getcpu_init(void) ...@@ -702,7 +702,7 @@ int vdso_getcpu_init(void)
node = cpu_to_node(cpu); node = cpu_to_node(cpu);
WARN_ON_ONCE(node > 0xffff); WARN_ON_ONCE(node > 0xffff);
val = (cpu & 0xfff) | ((node & 0xffff) << 16); val = (cpu & 0xffff) | ((node & 0xffff) << 16);
mtspr(SPRN_SPRG_VDSO_WRITE, val); mtspr(SPRN_SPRG_VDSO_WRITE, val);
get_paca()->sprg_vdso = val; get_paca()->sprg_vdso = val;
......
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