* Andy Lutomirski <luto@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
> 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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