| Message ID | 20200727165108.2378227-4-git@xen0n.name (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Refactor FTLBPar exception handling and add GSExc handler | expand |
On 2020/7/28 00:51, WANG Xuerui wrote: > Newer Loongson cores (Loongson-3A R2 and newer) use the > implementation-dependent ExcCode 16 to signal Loongson-specific > exceptions. The extended cause is put in the non-standard CP0.Diag1 > register which is CP0 Register 22 Select 1, called GSCause in Loongson > manuals. Inside is an exception code bitfield called GSExcCode, only > codes 0 to 6 inclusive are documented (so far, in the Loongson 3A3000 > User Manual, Volume 2). > > During experiments, it was found that some undocumented unprivileged > instructions can trigger the also-undocumented GSExcCode 8 on Loongson > 3A4000. Processor state is not corrupted, but we cannot continue without > further knowledge, and Loongson is not providing that information as of > this writing. So we send SIGILL on seeing this exception code to thwart > easy local DoS attacks. > > Other exception codes are made fatal, partly because of insufficient > knowledge, also partly because they are not as easily reproduced. None > of them are encountered in the wild with upstream kernels and userspace > so far. > > Some older cores (Loongson-3A1000 and Loongson-3B1500) have ExcCode 16 > too, but the semantic is equivalent to GSExcCode 0. Because the > respective manuals did not mention the CP0.Diag1 register or its read > behavior, these cores are not covered in this patch, as MFC0 from > non-existent CP0 registers is UNDEFINED according to the MIPS > architecture spec. > > Signed-off-by: WANG Xuerui <git@xen0n.name> > Cc: Huacai Chen <chenhc@lemote.com> > Cc: Jiaxun Yang <jiaxun.yang@flygoat.com> > Cc: Tiezhu Yang <yangtiezhu@loongson.cn> > --- > arch/mips/include/asm/cpu-features.h | 4 ++++ > arch/mips/include/asm/cpu.h | 1 + > arch/mips/include/asm/mipsregs.h | 3 +++ > arch/mips/kernel/cpu-probe.c | 3 +++ > arch/mips/kernel/genex.S | 7 ++++++ > arch/mips/kernel/traps.c | 35 ++++++++++++++++++++++++++++ > 6 files changed, 53 insertions(+) > > diff --git a/arch/mips/include/asm/cpu-features.h b/arch/mips/include/asm/cpu-features.h > index 0b1bc7ed913b..78cf7e300f12 100644 > --- a/arch/mips/include/asm/cpu-features.h > +++ b/arch/mips/include/asm/cpu-features.h > @@ -572,6 +572,10 @@ > # define cpu_has_ftlbparex __opt(MIPS_CPU_FTLBPAREX) > #endif > > +#ifndef cpu_has_gsexcex > +# define cpu_has_gsexcex __opt(MIPS_CPU_GSEXCEX) > +#endif > + > #ifdef CONFIG_SMP > /* > * Some systems share FTLB RAMs between threads within a core (siblings in > diff --git a/arch/mips/include/asm/cpu.h b/arch/mips/include/asm/cpu.h > index 3a4773714b29..1b4a67c84538 100644 > --- a/arch/mips/include/asm/cpu.h > +++ b/arch/mips/include/asm/cpu.h > @@ -426,6 +426,7 @@ enum cpu_type_enum { > #define MIPS_CPU_MM_FULL BIT_ULL(59) /* CPU supports write-through full merge */ > #define MIPS_CPU_MAC_2008_ONLY BIT_ULL(60) /* CPU Only support MAC2008 Fused multiply-add instruction */ > #define MIPS_CPU_FTLBPAREX BIT_ULL(61) /* CPU has FTLB parity exception */ > +#define MIPS_CPU_GSEXCEX BIT_ULL(62) /* CPU has GSExc exception */ > > /* > * CPU ASE encodings > diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h > index 5ba268266d16..4ddc12e4444a 100644 > --- a/arch/mips/include/asm/mipsregs.h > +++ b/arch/mips/include/asm/mipsregs.h > @@ -474,6 +474,9 @@ > /* Implementation specific trap codes used by MIPS cores */ > #define MIPS_EXCCODE_TLBPAR 16 /* TLB parity error exception */ > > +/* Implementation specific trap codes used by Loongson cores */ > +#define LOONGSON_EXCCODE_GSEXC 16 /* Loongson-specific exception */ > + > /* > * Bits in the coprocessor 0 config register. > */ > diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c > index 9e325862e810..9bb4a8732847 100644 > --- a/arch/mips/kernel/cpu-probe.c > +++ b/arch/mips/kernel/cpu-probe.c > @@ -2043,6 +2043,9 @@ static inline void cpu_probe_loongson(struct cpuinfo_mips *c, unsigned int cpu) > { > decode_configs(c); > > + /* All Loongson processors covered here define ExcCode 16 as GSExc. */ > + c->options |= MIPS_CPU_GSEXCEX; > + > switch (c->processor_id & PRID_IMP_MASK) { > case PRID_IMP_LOONGSON_64R: /* Loongson-64 Reduced */ > switch (c->processor_id & PRID_REV_MASK) { > diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S > index a1b966f3578e..a7fe30363dda 100644 > --- a/arch/mips/kernel/genex.S > +++ b/arch/mips/kernel/genex.S > @@ -498,6 +498,12 @@ NESTED(nmi_handler, PT_SIZE, sp) > KMODE > .endm > > + .macro __build_clear_gsexc > + MFC0 a1, CP0_DIAGNOSTIC1 This should be "mfc0" as the register is 32-bit. I'll send v4 soon; sorry for not noticing this. > + TRACE_IRQS_ON > + STI > + .endm > + > .macro __BUILD_silent exception > .endm > > @@ -556,6 +562,7 @@ NESTED(nmi_handler, PT_SIZE, sp) > BUILD_HANDLER fpe fpe fpe silent /* #15 */ > #endif > BUILD_HANDLER ftlb ftlb none silent /* #16 */ > + BUILD_HANDLER gsexc gsexc gsexc silent /* #16 */ > BUILD_HANDLER msa msa sti silent /* #21 */ > BUILD_HANDLER mdmx mdmx sti silent /* #22 */ > #ifdef CONFIG_HARDWARE_WATCHPOINTS > diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c > index 25a8a0d441be..fdb51e1f5f84 100644 > --- a/arch/mips/kernel/traps.c > +++ b/arch/mips/kernel/traps.c > @@ -90,6 +90,7 @@ extern asmlinkage void handle_tr(void); > extern asmlinkage void handle_msa_fpe(void); > extern asmlinkage void handle_fpe(void); > extern asmlinkage void handle_ftlb(void); > +extern asmlinkage void handle_gsexc(void); > extern asmlinkage void handle_msa(void); > extern asmlinkage void handle_mdmx(void); > extern asmlinkage void handle_watch(void); > @@ -1900,6 +1901,37 @@ asmlinkage void do_ftlb(void) > cache_parity_error(); > } > > +asmlinkage void do_gsexc(struct pt_regs *regs, u32 diag1) > +{ > + u32 exccode = (diag1 & LOONGSON_DIAG1_EXCCODE) >> > + LOONGSON_DIAG1_EXCCODE_SHIFT; > + enum ctx_state prev_state; > + > + prev_state = exception_enter(); > + > + switch (exccode) { > + case 0x08: > + /* Undocumented exception, will trigger on certain > + * also-undocumented instructions accessible from userspace. > + * Processor state is not otherwise corrupted, but currently > + * we don't know how to proceed. Maybe there is some > + * undocumented control flag to enable the instructions? > + */ > + force_sig(SIGILL); > + break; > + > + default: > + /* None of the other exceptions, documented or not, have > + * further details given; none are encountered in the wild > + * either. Panic in case some of them turn out to be fatal. > + */ > + show_regs(regs); > + panic("Unhandled Loongson exception - GSCause = %08x", diag1); > + } > + > + exception_exit(prev_state); > +} > + > /* > * SDBBP EJTAG debug exception handler. > * We skip the instruction and return to the next instruction. > @@ -2457,6 +2489,9 @@ void __init trap_init(void) > if (cpu_has_ftlbparex) > set_except_vector(MIPS_EXCCODE_TLBPAR, handle_ftlb); > > + if (cpu_has_gsexcex) > + set_except_vector(LOONGSON_EXCCODE_GSEXC, handle_gsexc); > + > if (cpu_has_rixiex) { > set_except_vector(EXCCODE_TLBRI, tlb_do_page_fault_0); > set_except_vector(EXCCODE_TLBXI, tlb_do_page_fault_0);
diff --git a/arch/mips/include/asm/cpu-features.h b/arch/mips/include/asm/cpu-features.h index 0b1bc7ed913b..78cf7e300f12 100644 --- a/arch/mips/include/asm/cpu-features.h +++ b/arch/mips/include/asm/cpu-features.h @@ -572,6 +572,10 @@ # define cpu_has_ftlbparex __opt(MIPS_CPU_FTLBPAREX) #endif +#ifndef cpu_has_gsexcex +# define cpu_has_gsexcex __opt(MIPS_CPU_GSEXCEX) +#endif + #ifdef CONFIG_SMP /* * Some systems share FTLB RAMs between threads within a core (siblings in diff --git a/arch/mips/include/asm/cpu.h b/arch/mips/include/asm/cpu.h index 3a4773714b29..1b4a67c84538 100644 --- a/arch/mips/include/asm/cpu.h +++ b/arch/mips/include/asm/cpu.h @@ -426,6 +426,7 @@ enum cpu_type_enum { #define MIPS_CPU_MM_FULL BIT_ULL(59) /* CPU supports write-through full merge */ #define MIPS_CPU_MAC_2008_ONLY BIT_ULL(60) /* CPU Only support MAC2008 Fused multiply-add instruction */ #define MIPS_CPU_FTLBPAREX BIT_ULL(61) /* CPU has FTLB parity exception */ +#define MIPS_CPU_GSEXCEX BIT_ULL(62) /* CPU has GSExc exception */ /* * CPU ASE encodings diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h index 5ba268266d16..4ddc12e4444a 100644 --- a/arch/mips/include/asm/mipsregs.h +++ b/arch/mips/include/asm/mipsregs.h @@ -474,6 +474,9 @@ /* Implementation specific trap codes used by MIPS cores */ #define MIPS_EXCCODE_TLBPAR 16 /* TLB parity error exception */ +/* Implementation specific trap codes used by Loongson cores */ +#define LOONGSON_EXCCODE_GSEXC 16 /* Loongson-specific exception */ + /* * Bits in the coprocessor 0 config register. */ diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c index 9e325862e810..9bb4a8732847 100644 --- a/arch/mips/kernel/cpu-probe.c +++ b/arch/mips/kernel/cpu-probe.c @@ -2043,6 +2043,9 @@ static inline void cpu_probe_loongson(struct cpuinfo_mips *c, unsigned int cpu) { decode_configs(c); + /* All Loongson processors covered here define ExcCode 16 as GSExc. */ + c->options |= MIPS_CPU_GSEXCEX; + switch (c->processor_id & PRID_IMP_MASK) { case PRID_IMP_LOONGSON_64R: /* Loongson-64 Reduced */ switch (c->processor_id & PRID_REV_MASK) { diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S index a1b966f3578e..a7fe30363dda 100644 --- a/arch/mips/kernel/genex.S +++ b/arch/mips/kernel/genex.S @@ -498,6 +498,12 @@ NESTED(nmi_handler, PT_SIZE, sp) KMODE .endm + .macro __build_clear_gsexc + MFC0 a1, CP0_DIAGNOSTIC1 + TRACE_IRQS_ON + STI + .endm + .macro __BUILD_silent exception .endm @@ -556,6 +562,7 @@ NESTED(nmi_handler, PT_SIZE, sp) BUILD_HANDLER fpe fpe fpe silent /* #15 */ #endif BUILD_HANDLER ftlb ftlb none silent /* #16 */ + BUILD_HANDLER gsexc gsexc gsexc silent /* #16 */ BUILD_HANDLER msa msa sti silent /* #21 */ BUILD_HANDLER mdmx mdmx sti silent /* #22 */ #ifdef CONFIG_HARDWARE_WATCHPOINTS diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c index 25a8a0d441be..fdb51e1f5f84 100644 --- a/arch/mips/kernel/traps.c +++ b/arch/mips/kernel/traps.c @@ -90,6 +90,7 @@ extern asmlinkage void handle_tr(void); extern asmlinkage void handle_msa_fpe(void); extern asmlinkage void handle_fpe(void); extern asmlinkage void handle_ftlb(void); +extern asmlinkage void handle_gsexc(void); extern asmlinkage void handle_msa(void); extern asmlinkage void handle_mdmx(void); extern asmlinkage void handle_watch(void); @@ -1900,6 +1901,37 @@ asmlinkage void do_ftlb(void) cache_parity_error(); } +asmlinkage void do_gsexc(struct pt_regs *regs, u32 diag1) +{ + u32 exccode = (diag1 & LOONGSON_DIAG1_EXCCODE) >> + LOONGSON_DIAG1_EXCCODE_SHIFT; + enum ctx_state prev_state; + + prev_state = exception_enter(); + + switch (exccode) { + case 0x08: + /* Undocumented exception, will trigger on certain + * also-undocumented instructions accessible from userspace. + * Processor state is not otherwise corrupted, but currently + * we don't know how to proceed. Maybe there is some + * undocumented control flag to enable the instructions? + */ + force_sig(SIGILL); + break; + + default: + /* None of the other exceptions, documented or not, have + * further details given; none are encountered in the wild + * either. Panic in case some of them turn out to be fatal. + */ + show_regs(regs); + panic("Unhandled Loongson exception - GSCause = %08x", diag1); + } + + exception_exit(prev_state); +} + /* * SDBBP EJTAG debug exception handler. * We skip the instruction and return to the next instruction. @@ -2457,6 +2489,9 @@ void __init trap_init(void) if (cpu_has_ftlbparex) set_except_vector(MIPS_EXCCODE_TLBPAR, handle_ftlb); + if (cpu_has_gsexcex) + set_except_vector(LOONGSON_EXCCODE_GSEXC, handle_gsexc); + if (cpu_has_rixiex) { set_except_vector(EXCCODE_TLBRI, tlb_do_page_fault_0); set_except_vector(EXCCODE_TLBXI, tlb_do_page_fault_0);
Newer Loongson cores (Loongson-3A R2 and newer) use the implementation-dependent ExcCode 16 to signal Loongson-specific exceptions. The extended cause is put in the non-standard CP0.Diag1 register which is CP0 Register 22 Select 1, called GSCause in Loongson manuals. Inside is an exception code bitfield called GSExcCode, only codes 0 to 6 inclusive are documented (so far, in the Loongson 3A3000 User Manual, Volume 2). During experiments, it was found that some undocumented unprivileged instructions can trigger the also-undocumented GSExcCode 8 on Loongson 3A4000. Processor state is not corrupted, but we cannot continue without further knowledge, and Loongson is not providing that information as of this writing. So we send SIGILL on seeing this exception code to thwart easy local DoS attacks. Other exception codes are made fatal, partly because of insufficient knowledge, also partly because they are not as easily reproduced. None of them are encountered in the wild with upstream kernels and userspace so far. Some older cores (Loongson-3A1000 and Loongson-3B1500) have ExcCode 16 too, but the semantic is equivalent to GSExcCode 0. Because the respective manuals did not mention the CP0.Diag1 register or its read behavior, these cores are not covered in this patch, as MFC0 from non-existent CP0 registers is UNDEFINED according to the MIPS architecture spec. Signed-off-by: WANG Xuerui <git@xen0n.name> Cc: Huacai Chen <chenhc@lemote.com> Cc: Jiaxun Yang <jiaxun.yang@flygoat.com> Cc: Tiezhu Yang <yangtiezhu@loongson.cn> --- arch/mips/include/asm/cpu-features.h | 4 ++++ arch/mips/include/asm/cpu.h | 1 + arch/mips/include/asm/mipsregs.h | 3 +++ arch/mips/kernel/cpu-probe.c | 3 +++ arch/mips/kernel/genex.S | 7 ++++++ arch/mips/kernel/traps.c | 35 ++++++++++++++++++++++++++++ 6 files changed, 53 insertions(+)