From: Milton Miller miltonm@us.ibm.com
[ Upstream commit a9f675f950a07d5c1dbcbb97aabac56f5ed085e3 ]
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 Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20200715233704.1352257-1-anton@ozlabs.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 65b3bdb99f0ba..31ab6eb61e26e 100644 --- a/arch/powerpc/kernel/vdso.c +++ b/arch/powerpc/kernel/vdso.c @@ -705,7 +705,7 @@ 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;