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From: Andy Lutomirski <luto@kernel.org>
To: X86 ML <x86@kernel.org>
Cc: KVM list <kvm@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	xen-devel <Xen-devel@lists.xen.org>,
	Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Arjan van de Ven <arjan@linux.intel.com>
Subject: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops
Date: Sat, 12 Mar 2016 10:08:49 -0800	[thread overview]
Message-ID: <a3b871a4eb533340d04255409dfecc94f88c647d.1457805972.git.luto__2957.41268569163$1457806216$gmane$org@kernel.org> (raw)
In-Reply-To: <cover.1457805972.git.luto@kernel.org>
In-Reply-To: <cover.1457805972.git.luto@kernel.org>

This demotes an OOPS and likely panic due to a failed non-"safe" MSR
access to a WARN_ONCE and, for RDMSR, a return value of zero.  If
panic_on_oops is set, then failed unsafe MSR accesses will still
oops and panic.

To be clear, this type of failure should *not* happen.  This patch
exists to minimize the chance of nasty undebuggable failures due on
systems that used to work due to a now-fixed CONFIG_PARAVIRT=y bug.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/include/asm/msr.h | 10 ++++++++--
 arch/x86/mm/extable.c      | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 93fb7c1cffda..1487054a1a70 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -92,7 +92,10 @@ static inline unsigned long long native_read_msr(unsigned int msr)
 {
 	DECLARE_ARGS(val, low, high);
 
-	asm volatile("rdmsr" : EAX_EDX_RET(val, low, high) : "c" (msr));
+	asm volatile("1: rdmsr\n"
+		     "2:\n"
+		     _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_rdmsr_unsafe)
+		     : EAX_EDX_RET(val, low, high) : "c" (msr));
 	if (msr_tracepoint_active(__tracepoint_read_msr))
 		do_trace_read_msr(msr, EAX_EDX_VAL(val, low, high), 0);
 	return EAX_EDX_VAL(val, low, high);
@@ -119,7 +122,10 @@ static inline unsigned long long native_read_msr_safe(unsigned int msr,
 static inline void native_write_msr(unsigned int msr,
 				    unsigned low, unsigned high)
 {
-	asm volatile("wrmsr" : : "c" (msr), "a"(low), "d" (high) : "memory");
+	asm volatile("1: wrmsr\n"
+		     "2:\n"
+		     _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_wrmsr_unsafe)
+		     : : "c" (msr), "a"(low), "d" (high) : "memory");
 	if (msr_tracepoint_active(__tracepoint_read_msr))
 		do_trace_write_msr(msr, ((u64)high << 32 | low), 0);
 }
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 9dd7e4b7fcde..9e6749b34524 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -49,6 +49,39 @@ bool ex_handler_ext(const struct exception_table_entry *fixup,
 }
 EXPORT_SYMBOL(ex_handler_ext);
 
+bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup,
+			     struct pt_regs *regs, int trapnr)
+{
+	WARN_ONCE(1, "unchecked MSR access error: RDMSR from 0x%x",
+		  (unsigned int)regs->cx);
+
+	/* If panic_on_oops is set, don't try to recover. */
+	if (panic_on_oops)
+		return false;
+
+	regs->ip = ex_fixup_addr(fixup);
+	regs->ax = 0;
+	regs->dx = 0;
+	return true;
+}
+EXPORT_SYMBOL(ex_handler_rdmsr_unsafe);
+
+bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup,
+			     struct pt_regs *regs, int trapnr)
+{
+	WARN_ONCE(1, "unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x)\n",
+		  (unsigned int)regs->cx,
+		  (unsigned int)regs->dx, (unsigned int)regs->ax);
+
+	/* If panic_on_oops is set, don't try to recover. */
+	if (panic_on_oops)
+		return false;
+
+	regs->ip = ex_fixup_addr(fixup);
+	return true;
+}
+EXPORT_SYMBOL(ex_handler_wrmsr_unsafe);
+
 bool ex_has_fault_handler(unsigned long ip)
 {
 	const struct exception_table_entry *e;
-- 
2.5.0


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  parent reply	other threads:[~2016-03-12 18:08 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <cover.1457805972.git.luto@kernel.org>
2016-03-12 18:08 ` [PATCH v4 1/5] x86/paravirt: Add _safe to the read_msr and write_msr PV hooks Andy Lutomirski
2016-03-12 18:08 ` Andy Lutomirski [this message]
2016-03-12 18:08 ` [PATCH v4 3/5] x86/paravirt: Add paravirt_{read, write}_msr Andy Lutomirski
2016-03-12 18:08 ` [PATCH v4 4/5] x86/paravirt: Make "unsafe" MSR accesses unsafe even if PARAVIRT=y Andy Lutomirski
2016-03-12 18:08 ` [PATCH v4 5/5] x86/msr: Set the return value to zero when native_rdmsr_safe fails Andy Lutomirski
     [not found] ` <7e72cd6ce08b946872a462fad13eca1810b8671d.1457805972.git.luto@kernel.org>
2016-03-14 11:57   ` [PATCH v4 1/5] x86/paravirt: Add _safe to the read_msr and write_msr PV hooks Borislav Petkov
     [not found]   ` <20160314115729.GC15800@pd.tnic>
2016-03-14 17:07     ` Andy Lutomirski
     [not found] ` <a3b871a4eb533340d04255409dfecc94f88c647d.1457805972.git.luto@kernel.org>
2016-03-14 12:02   ` [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Borislav Petkov
     [not found]   ` <20160314120202.GD15800@pd.tnic>
2016-03-14 17:05     ` Andy Lutomirski
     [not found]     ` <CALCETrW6E0Nz6gSmRKTvHbQDhnHVpuhzmgZB1nZ3m-DL-Bt=tQ@mail.gmail.com>
2016-03-14 17:11       ` Linus Torvalds
2016-03-14 17:17         ` Andy Lutomirski
     [not found]         ` <CALCETrXhXPj_b6rUMn=SR0QwE92rL=k5DCFraZwBj9FpUgadYw@mail.gmail.com>
2016-03-14 18:04           ` Linus Torvalds
     [not found]           ` <CA+55aFwr80aZ3-1H4VPB5=jeU_Yt=hYFfFvZC5-cNXzgXxGf3A@mail.gmail.com>
2016-03-14 18:10             ` Andy Lutomirski
2016-03-14 18:10             ` Linus Torvalds
     [not found]             ` <CALCETrV16vh5U0TRzdroSTBR_QHDX1C78t0DDW9qtKjOmV+2sQ@mail.gmail.com>
2016-03-14 18:15               ` Linus Torvalds
     [not found]               ` <CA+55aFz=PdvMWSsXExrpQC2UV6aLS+=+VOo+K4=njQoU5B9hgA@mail.gmail.com>
2016-03-14 18:24                 ` Andy Lutomirski
     [not found]                 ` <CALCETrXAAOcGP7DK+7aKn=2pu=SQ0n_PhG9bV4DcoYcv9epn4A@mail.gmail.com>
2016-03-14 18:40                   ` Linus Torvalds
     [not found]                   ` <CA+55aFy2dNgBJwjd+fRUYQf9OxqGkkcjUEarv+o3QSFTJ6+gJQ@mail.gmail.com>
2016-03-14 18:48                     ` Andy Lutomirski
     [not found]                     ` <CALCETrWxSBwwFTFsRoR_9AVBoC0iJ1pdWwOq_cnFf3NHUpG4QA@mail.gmail.com>
2016-03-15 10:22                       ` Ingo Molnar
     [not found]                       ` <20160315102230.GB23406@gmail.com>
2016-03-15 10:26                         ` Ingo Molnar
2016-03-14 20:18               ` Peter Zijlstra
2016-03-15 10:21             ` Ingo Molnar
2016-03-14 14:32 ` [PATCH v4 0/5] [PATCH v3 0/5] Improve non-"safe" MSR access failure handling Boris Ostrovsky

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