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Groups > linux.kernel > #1356506
| From | Andy Lutomirski <luto@kernel.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops |
| Date | 2016-03-12 19:10 +0100 |
| Message-ID | <rbW9d-1Em-33@gated-at.bofh.it> (permalink) |
| References | <rbW9c-1Em-5@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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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[PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Andy Lutomirski <luto@kernel.org> - 2016-03-12 19:10 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Borislav Petkov <bp@alien8.de> - 2016-03-14 13:10 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Andy Lutomirski <luto@amacapital.net> - 2016-03-14 18:10 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Andy Lutomirski <luto@amacapital.net> - 2016-03-14 18:20 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-14 19:10 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-14 19:20 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-14 19:20 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Andy Lutomirski <luto@amacapital.net> - 2016-03-14 19:30 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Andy Lutomirski <luto@amacapital.net> - 2016-03-14 19:50 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Ingo Molnar <mingo@kernel.org> - 2016-03-15 11:30 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Ingo Molnar <mingo@kernel.org> - 2016-03-15 11:30 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-14 19:50 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Andy Lutomirski <luto@amacapital.net> - 2016-03-14 19:20 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Peter Zijlstra <peterz@infradead.org> - 2016-03-14 21:20 +0100
Re: [PATCH v4 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Ingo Molnar <mingo@kernel.org> - 2016-03-15 11:30 +0100
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