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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next prev 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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