| Message ID | 35f2f107e0d85473a0e66c08f93d571a9c72b7fc.1457723023.git.luto@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
* Andy Lutomirski <luto@kernel.org> 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
* Andy Lutomirski <luto@kernel.org> 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 <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..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
On Sat, Mar 12, 2016 at 7:36 AM, Ingo Molnar <mingo@kernel.org> wrote: > > * Andy Lutomirski <luto@kernel.org> 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 <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..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
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;
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 <luto@kernel.org> --- arch/x86/include/asm/msr.h | 10 ++++++++-- arch/x86/mm/extable.c | 33 +++++++++++++++++++++++++++++++++ 2 files changed, 41 insertions(+), 2 deletions(-)