[PATCH v2] MIPS: vdso: flush the vdso data page to update it on all processes

Hauke Mehrtens
2016-02-21T17:27:22Z

Without flushing the vdso data page the vdso call is working on dated
or unsynced data. This resulted in problems where the clock_gettime
vdso call returned a time 6 seconds later after a 3 seconds sleep,
while the syscall reported a time 3 sounds later, like expected. This
happened very often and I got these ping results for example:

root@OpenWrt:/# ping 192.168.1.255
PING 192.168.1.255 (192.168.1.255): 56 data bytes
64 bytes from 192.168.1.3: seq=0 ttl=64 time=0.688 ms
64 bytes from 192.168.1.3: seq=1 ttl=64 time=4294172.045 ms
64 bytes from 192.168.1.3: seq=2 ttl=64 time=4293968.105 ms
64 bytes from 192.168.1.3: seq=3 ttl=64 time=4294055.920 ms
64 bytes from 192.168.1.3: seq=4 ttl=64 time=4294671.913 ms

This was tested on a Lantiq/Intel VRX288 (MIPS BE 34Kc V5.6 CPU with
two VPEs)

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: <stable@vger.kernel.org> # v4.4+
---
arch/mips/kernel/vdso.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c
index 975e997..8b0d974 100644
--- a/arch/mips/kernel/vdso.c
+++ b/arch/mips/kernel/vdso.c
@@ -20,6 +20,8 @@
#include <linux/timekeeper_internal.h>

#include <asm/abi.h>
+#include <asm/cacheflush.h>
+#include <asm/page.h>
#include <asm/vdso.h>

/* Kernel-provided data used by the VDSO. */
@@ -85,6 +87,8 @@ void update_vsyscall(struct timekeeper *tk)
}

vdso_data_write_end(&vdso_data);
+ flush_cache_vmap((unsigned long)&vdso_data,
+ (unsigned long)&vdso_data + sizeof(vdso_data));
}

void update_vsyscall_tz(void)
@@ -93,6 +97,8 @@ void update_vsyscall_tz(void)
vdso_data.tz_minuteswest = sys_tz.tz_minuteswest;
vdso_data.tz_dsttime = sys_tz.tz_dsttime;
}
+ flush_cache_vmap((unsigned long)&vdso_data,
+ (unsigned long)&vdso_data + sizeof(vdso_data));
}

int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
--
2.7.0