Commit 5a5525b0 authored Nov 18, 2019 by Heiko Carstens Committed by Vasily Gorbik Nov 30, 2019

s390/vdso: fix getcpu



getcpu reads the required values for cpu and node with two
instructions. This might lead to an inconsistent result if user space
gets preempted and migrated to a different CPU between the two
instructions.

Fix this by using just a single instruction to read both values at
once.

This is currently rather a theoretical bug, since there is no real
NUMA support available (except for NUMA emulation).

Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

parent a2308c11

arch/s390/include/asm/vdso.h

+11 −2

Original line number	Diff line number	Diff line
		@@ -41,8 +41,17 @@ struct vdso_data {
		struct vdso_per_cpu_data {
		__u64 ectg_timer_base;
		__u64 ectg_user_time;
		__u32 cpu_nr;
		/*
		* Note: node_id and cpu_nr must be at adjacent memory locations.
		* VDSO userspace must read both values with a single instruction.
		*/
		union {
		__u64 getcpu_val;
		struct {
		__u32 node_id;
		__u32 cpu_nr;
		};
		};
		};

		extern struct vdso_data *vdso_data;

arch/s390/kernel/asm-offsets.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -78,8 +78,7 @@ int main(void)
		OFFSET(__VDSO_TS_END, vdso_data, ts_end);
		OFFSET(__VDSO_ECTG_BASE, vdso_per_cpu_data, ectg_timer_base);
		OFFSET(__VDSO_ECTG_USER, vdso_per_cpu_data, ectg_user_time);
		OFFSET(__VDSO_CPU_NR, vdso_per_cpu_data, cpu_nr);
		OFFSET(__VDSO_NODE_ID, vdso_per_cpu_data, node_id);
		OFFSET(__VDSO_GETCPU_VAL, vdso_per_cpu_data, getcpu_val);
		BLANK();
		/* constants used by the vdso */
		DEFINE(__CLOCK_REALTIME, CLOCK_REALTIME);

arch/s390/kernel/vdso32/getcpu.S

+1 −3

Original line number	Diff line number	Diff line
		@@ -16,10 +16,8 @@
		.type __kernel_getcpu,@function
		__kernel_getcpu:
		CFI_STARTPROC
		la %r4,0
		sacf 256
		l %r5,__VDSO_CPU_NR(%r4)
		l %r4,__VDSO_NODE_ID(%r4)
		lm %r4,%r5,__VDSO_GETCPU_VAL(%r0)
		sacf 0
		ltr %r2,%r2
		jz 2f

arch/s390/kernel/vdso64/getcpu.S

+1 −3

Original line number	Diff line number	Diff line
		@@ -16,10 +16,8 @@
		.type __kernel_getcpu,@function
		__kernel_getcpu:
		CFI_STARTPROC
		la %r4,0
		sacf 256
		l %r5,__VDSO_CPU_NR(%r4)
		l %r4,__VDSO_NODE_ID(%r4)
		lm %r4,%r5,__VDSO_GETCPU_VAL(%r0)
		sacf 0
		ltgr %r2,%r2
		jz 2f