Re: [Xen-devel] [PATCH v3 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops
On Sat, Mar 12, 2016 at 7:36 AM, Ingo Molnar wrote:
>
> * Andy Lutomirski wrote:
>
>> This demotes an OOPS and likely panic due to a failed non-"safe" MSR
>> access to a WARN 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
>> ---
>> 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..f310714e6e6d 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(1, "unsafe MSR access error: RDMSR from 0x%x",
>> + (unsigned int)regs->cx);
>
> Btw., instead of the safe/unsafe naming (which has an emotional and security
> secondary attribute), shouldn't we move this over to a _check() (or
> _checking())
> naming instead that we do in other places in the kernel?
>
> I.e.:
>
> rdmsr(msr, l, h);
>
> and:
>
> if (rdmsr_check(msr, l, h)) {
> ...
> }
>
> and then we could name the helpers as _check() and _nocheck() - which is
> neutral
> naming.
Will do as a separate followup series.
At least with this series applied, the functions named _safe all point
to each other correctly.
--Andy
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Re: [Xen-devel] [PATCH v3 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops
* Andy Lutomirski wrote:
> This demotes an OOPS and likely panic due to a failed non-"safe" MSR
> access to a WARN 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
> ---
> 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..f310714e6e6d 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(1, "unsafe MSR access error: RDMSR from 0x%x",
> + (unsigned int)regs->cx);
Btw., instead of the safe/unsafe naming (which has an emotional and security
secondary attribute), shouldn't we move this over to a _check() (or
_checking())
naming instead that we do in other places in the kernel?
I.e.:
rdmsr(msr, l, h);
and:
if (rdmsr_check(msr, l, h)) {
...
}
and then we could name the helpers as _check() and _nocheck() - which is
neutral
naming.
Thanks,
Ingo
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Re: [Xen-devel] [PATCH v3 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops
* Andy Lutomirski wrote:
> +bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup,
> + struct pt_regs *regs, int trapnr)
> +{
> + WARN(1, "unsafe MSR access error: RDMSR from 0x%x",
> + (unsigned int)regs->cx);
Please make this WARN_ONCE(). There's no point in locking up the system with
WARN() spam, should this trigger frequently.
> + WARN(1, "unsafe 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);
Ditto.
Thanks,
Ingo
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[Xen-devel] [PATCH v3 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops
This demotes an OOPS and likely panic due to a failed non-"safe" MSR
access to a WARN 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
---
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..f310714e6e6d 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(1, "unsafe 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(1, "unsafe 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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