linux-kernel - [RFC 1/6] vdso/extable: fix calculation of base

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Message-Id: <20210225072910.2811795-2-namit@vmware.com>
Date:   Wed, 24 Feb 2021 23:29:05 -0800
From:   Nadav Amit <nadav.amit@...il.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Hugh Dickins <hughd@...gle.com>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Nadav Amit <namit@...are.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org
Subject: [RFC 1/6] vdso/extable: fix calculation of base

From: Nadav Amit <namit@...are.com>

Apparently, the assembly considers __ex_table as the location when the
pushsection directive was issued. Therefore when there is more than a
single entry in the vDSO exception table, the calculations of the base
and fixup are wrong.

Fix the calculations of the expected fault IP and new IP by adjusting
the base after each entry.

Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sean Christopherson <seanjc@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: x86@...nel.org
Signed-off-by: Nadav Amit <namit@...are.com>
---
 arch/x86/entry/vdso/extable.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/entry/vdso/extable.c b/arch/x86/entry/vdso/extable.c
index afcf5b65beef..c81e78636220 100644
--- a/arch/x86/entry/vdso/extable.c
+++ b/arch/x86/entry/vdso/extable.c
@@ -32,7 +32,7 @@ bool fixup_vdso_exception(struct pt_regs *regs, int trapnr,
 	nr_entries = image->extable_len / (sizeof(*extable));
 	extable = image->extable;
 
-	for (i = 0; i < nr_entries; i++) {
+	for (i = 0; i < nr_entries; i++, base += sizeof(*extable)) {
 		if (regs->ip == base + extable[i].insn) {
 			regs->ip = base + extable[i].fixup;
 			regs->di = trapnr;
-- 
2.25.1