[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH for-4.18] x86/time: Fix UBSAN failure in __update_vcpu_system_time()
As reported: (XEN) ================================================================================ (XEN) UBSAN: Undefined behaviour in arch/x86/time.c:1542:32 (XEN) member access within null pointer of type 'union vcpu_info_t' (XEN) ----[ Xen-4.19-unstable x86_64 debug=y ubsan=y Not tainted ]---- ... (XEN) Xen call trace: (XEN) [<ffff82d040345036>] R common/ubsan/ubsan.c#ubsan_epilogue+0xa/0xd2 (XEN) [<ffff82d0403456e8>] F __ubsan_handle_type_mismatch+0x133/0x49b (XEN) [<ffff82d040345b4a>] F __ubsan_handle_type_mismatch_v1+0xfa/0xfc (XEN) [<ffff82d040623356>] F arch/x86/time.c#__update_vcpu_system_time+0x212/0x30f (XEN) [<ffff82d040623461>] F update_vcpu_system_time+0xe/0x10 (XEN) [<ffff82d04062389d>] F arch/x86/time.c#local_time_calibration+0x1f7/0x523 (XEN) [<ffff82d0402a64b5>] F common/softirq.c#__do_softirq+0x1f4/0x31a (XEN) [<ffff82d0402a67ad>] F do_softirq+0x13/0x15 (XEN) [<ffff82d0405a95dc>] F arch/x86/domain.c#idle_loop+0x2e0/0x367 (XEN) (XEN) ================================================================================ It is not valid to derive a pointer from vcpu_info() prior to checking that the underlying map pointer is good. Reorder actions so the NULL pointer check is first. Fixes: 20279afd7323 ("x86: split populating of struct vcpu_time_info into a separate function") Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> --- CC: Jan Beulich <JBeulich@xxxxxxxx> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx> CC: Wei Liu <wl@xxxxxxx> CC: Henry Wang <Henry.Wang@xxxxxxx> 4.18 blocker, or we'll need to issue an XSA/CVE. --- xen/arch/x86/time.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c index d0b0986509b2..6d33edd0addc 100644 --- a/xen/arch/x86/time.c +++ b/xen/arch/x86/time.c @@ -1539,12 +1539,14 @@ static void collect_time_info(const struct vcpu *v, static void __update_vcpu_system_time(struct vcpu *v, int force) { - struct vcpu_time_info *u = &vcpu_info(v, time), _u; + struct vcpu_time_info *u, _u; const struct domain *d = v->domain; if ( !v->vcpu_info_area.map ) return; + u = &vcpu_info(v, time); + collect_time_info(v, &_u); /* Don't bother unless timestamp record has changed or we are forced. */ base-commit: 7befef87cc9b1bb8ca15d866ce1ecd9165ccb58c -- 2.30.2
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