linux-kernel - [PATCH 2/2] drivers/hv: correct tsc page sequence invalid value

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1447880710-9751-2-git-send-email-kys@microsoft.com>
Date:	Wed, 18 Nov 2015 13:05:10 -0800
From:	"K. Y. Srinivasan" <kys@...rosoft.com>
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
	vkuznets@...hat.com, jasowang@...hat.com
Cc:	Andrey Smetanin <asmetanin@...tuozzo.com>,
	"Denis V. Lunev" <den@...nvz.org>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: [PATCH 2/2] drivers/hv: correct tsc page sequence invalid value

From: Andrey Smetanin <asmetanin@...tuozzo.com>

Hypervisor Top Level Functional Specification v3/4 says
that TSC page sequence value = -1(0xFFFFFFFF) is used to
indicate that TSC page no longer reliable source of reference
timer. Unfortunately, we found that Windows Hyper-V guest
side implementation uses sequence value = 0 to indicate
that Tsc page no longer valid. This is clearly visible
inside Windows 2012R2 ntoskrnl.exe HvlGetReferenceTime()
function dissassembly:

HvlGetReferenceTime proc near
                 xchg    ax, ax
loc_1401C3132:
                 mov     rax, cs:HvlpReferenceTscPage
                 mov     r9d, [rax]
                 test    r9d, r9d
                 jz      short loc_1401C3176
                 rdtsc
                 mov     rcx, cs:HvlpReferenceTscPage
                 shl     rdx, 20h
                 or      rdx, rax
                 mov     rax, [rcx+8]
                 mov     rcx, cs:HvlpReferenceTscPage
                 mov     r8, [rcx+10h]
                 mul     rdx
                 mov     rax, cs:HvlpReferenceTscPage
                 add     rdx, r8
                 mov     ecx, [rax]
                 cmp     ecx, r9d
                 jnz     short loc_1401C3132
                 jmp     short loc_1401C3184
loc_1401C3176:
                 mov     ecx, 40000020h
                 rdmsr
                 shl     rdx, 20h
                 or      rdx, rax
loc_1401C3184:
                 mov     rax, rdx
                 retn
HvlGetReferenceTime endp

This patch aligns Tsc page invalid sequence value with
Windows Hyper-V guest implementation which is more
compatible with both Hyper-V hypervisor and KVM hypervisor.

Signed-off-by: Andrey Smetanin <asmetanin@...tuozzo.com>
Signed-off-by: Denis V. Lunev <den@...nvz.org>
CC: "K. Y. Srinivasan" <kys@...rosoft.com>
CC: Haiyang Zhang <haiyangz@...rosoft.com>
CC: Vitaly Kuznetsov <vkuznets@...hat.com>

Signed-off-by: Denis V. Lunev <den@...nvz.org>
Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
---
 drivers/hv/hv.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index 7a06933..1db9556 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -140,7 +140,7 @@ static cycle_t read_hv_clock_tsc(struct clocksource *arg)
 	cycle_t current_tick;
 	struct ms_hyperv_tsc_page *tsc_pg = hv_context.tsc_page;
 
-	if (tsc_pg->tsc_sequence != -1) {
+	if (tsc_pg->tsc_sequence != 0) {
 		/*
 		 * Use the tsc page to compute the value.
 		 */
@@ -162,7 +162,7 @@ static cycle_t read_hv_clock_tsc(struct clocksource *arg)
 			if (tsc_pg->tsc_sequence == sequence)
 				return current_tick;
 
-			if (tsc_pg->tsc_sequence != -1)
+			if (tsc_pg->tsc_sequence != 0)
 				continue;
 			/*
 			 * Fallback using MSR method.
-- 
1.7.4.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/