+++ /dev/null
-From 72ce778007e57e8996b4bebdec738fc5e1145fd2 Mon Sep 17 00:00:00 2001
-From: Thomas Gleixner <tglx@linutronix.de>
-Date: Sat, 6 Jun 2020 23:51:16 +0200
-Subject: lib/vdso: Provide sanity check for cycles (again)
-
-From: Thomas Gleixner <tglx@linutronix.de>
-
-commit 72ce778007e57e8996b4bebdec738fc5e1145fd2 upstream.
-
-The original x86 VDSO implementation checked for the validity of the clock
-source read by testing whether the returned signed cycles value is less
-than zero. This check was also used by the vdso read function to signal
-that the current selected clocksource is not VDSO capable.
-
-During the rework of the VDSO code the check was removed and replaced with
-a check for the clocksource mode being != NONE.
-
-This turned out to be a mistake because the check is necessary for paravirt
-and hyperv clock sources. The reason is that these clock sources have their
-own internal sequence counter to validate the clocksource at the point of
-reading it. This is necessary because the hypervisor can invalidate the
-clocksource asynchronously so a check during the VDSO data update is not
-sufficient. Having a separate indicator for the validity is slower than
-just validating the cycles value. The check for it being negative turned
-out to be the fastest implementation and safe as it would require an uptime
-of ~73 years with a 4GHz counter frequency to result in a false positive.
-
-Add an optional function to validate the cycles with a default
-implementation which allows the compiler to optimize it out for
-architectures which do not require it.
-
-Fixes: 5d51bee725cc ("clocksource: Add common vdso clock mode storage")
-Reported-by: Miklos Szeredi <miklos@szeredi.hu>
-Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
-Tested-by: Miklos Szeredi <mszeredi@redhat.com>
-Cc: stable@vger.kernel.org
-Link: https://lkml.kernel.org/r/20200606221531.963970768@linutronix.de
-Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-
----
- lib/vdso/gettimeofday.c | 11 +++++++++++
- 1 file changed, 11 insertions(+)
-
---- a/lib/vdso/gettimeofday.c
-+++ b/lib/vdso/gettimeofday.c
-@@ -38,6 +38,13 @@ static inline bool vdso_clocksource_ok(c
- }
- #endif
-
-+#ifndef vdso_cycles_ok
-+static inline bool vdso_cycles_ok(u64 cycles)
-+{
-+ return true;
-+}
-+#endif
-+
- #ifdef CONFIG_TIME_NS
- static int do_hres_timens(const struct vdso_data *vdns, clockid_t clk,
- struct __kernel_timespec *ts)
-@@ -62,6 +69,8 @@ static int do_hres_timens(const struct v
- return -1;
-
- cycles = __arch_get_hw_counter(vd->clock_mode);
-+ if (unlikely(!vdso_cycles_ok(cycles)))
-+ return -1;
- ns = vdso_ts->nsec;
- last = vd->cycle_last;
- ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult);
-@@ -130,6 +139,8 @@ static __always_inline int do_hres(const
- return -1;
-
- cycles = __arch_get_hw_counter(vd->clock_mode);
-+ if (unlikely(!vdso_cycles_ok(cycles)))
-+ return -1;
- ns = vdso_ts->nsec;
- last = vd->cycle_last;
- ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult);
s390-bpf-maintain-8-byte-stack-alignment.patch
kasan-stop-tests-being-eliminated-as-dead-code-with-.patch
string.h-fix-incompatibility-between-fortify_source-.patch
-lib-vdso-provide-sanity-check-for-cycles-again.patch
projects / thirdparty / kernel / stable-queue.git / commitdiff
