Linux-MIPS Archive on lore.kernel.org
 help / color / Atom feed
* [PATCH v3 0/3] Refactor FTLBPar exception handling and add GSExc handler
@ 2020-07-27 16:51 WANG Xuerui
  2020-07-27 16:51 ` [PATCH v3 1/3] MIPS: only register FTLBPar exception handler for supported models WANG Xuerui
                   ` (3 more replies)
  0 siblings, 4 replies; 6+ messages in thread
From: WANG Xuerui @ 2020-07-27 16:51 UTC (permalink / raw)
  To: linux-mips; +Cc: WANG Xuerui

It was found that some undocumented unprivileged instructions could
crash the kernel with a "FTLB parity error" on Loongson-3A4000, but the
error registers were garbage:

[  896.970419] FTLB error exception, cp0_ecc=0x00000002:
[  896.975446] cp0_errorepc == ffffffffffffffff
[  896.979755] c0_cacheerr == 00000000
[  896.983277] Decoded c0_cacheerr: primary cache fault in insn reference.
[  896.989963] Cache error exception:
[  896.993396] cp0_errorepc == ffffffffffffffff
[  896.997707] c0_cacheerr == 00000000
[  897.001228] Decoded c0_cacheerr: primary cache fault in insn reference.
[  897.007916] Error bits: 
[  897.010467] IDX: 0x00000000
[  897.013284] Kernel panic - not syncing: Can't handle the cache error!
[  897.019807] ---[ end Kernel panic - not syncing: Can't handle the cache error! ]---

Turns out the FTLBPar exception code is actually implementation-specific.
On Loongson cores the exception is "GSExc" instead, and is non-fatal in
Loongson's linux-3.10 fork. So we dynamically register the correct handler
for the exception, and do not panic on the specific undocumented case.

P.S. There is not much space left in the cpuinfo_mips.options flag. We
should consider moving to something like x86's feature flags that is
extensible.

v3:
- Simplified declaration of cpu_has_gsexcex, as suggested by Huacai

v2:
- Removed stray GSExc logic in cpu_probe_legacy, pointed out by Huacai

WANG Xuerui (3):
  MIPS: only register FTLBPar exception handler for supported models
  MIPS: add definitions for Loongson-specific CP0.Diag1 register
  MIPS: handle Loongson-specific GSExc exception

 arch/mips/include/asm/cpu-features.h |  8 ++++++
 arch/mips/include/asm/cpu.h          |  2 ++
 arch/mips/include/asm/mipsregs.h     | 11 ++++++++
 arch/mips/kernel/cpu-probe.c         | 16 ++++++++++++
 arch/mips/kernel/genex.S             |  7 +++++
 arch/mips/kernel/traps.c             | 38 +++++++++++++++++++++++++++-
 6 files changed, 81 insertions(+), 1 deletion(-)

-- 
2.25.1


^ permalink raw reply	[flat|nested] 6+ messages in thread

* [PATCH v3 1/3] MIPS: only register FTLBPar exception handler for supported models
  2020-07-27 16:51 [PATCH v3 0/3] Refactor FTLBPar exception handling and add GSExc handler WANG Xuerui
@ 2020-07-27 16:51 ` WANG Xuerui
  2020-07-27 16:51 ` [PATCH v3 2/3] MIPS: add definitions for Loongson-specific CP0.Diag1 register WANG Xuerui
                   ` (2 subsequent siblings)
  3 siblings, 0 replies; 6+ messages in thread
From: WANG Xuerui @ 2020-07-27 16:51 UTC (permalink / raw)
  To: linux-mips
  Cc: WANG Xuerui, Leonid Yegoshin, Markos Chandras, John Crispin, Paul Burton

Previously ExcCode 16 is unconditionally treated as the FTLB parity
exception (FTLBPar), but in fact its semantic is implementation-
dependent. Looking at various manuals it seems the FTLBPar exception is
only present on some recent MIPS Technologies cores, so only register
the handler on these.

Fixes: 75b5b5e0a262790f ("MIPS: Add support for FTLBs")
Signed-off-by: WANG Xuerui <git@xen0n.name>
Cc: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: John Crispin <blogic@openwrt.org>
Cc: Paul Burton <paulburton@kernel.org>
---
 arch/mips/include/asm/cpu-features.h |  4 ++++
 arch/mips/include/asm/cpu.h          |  1 +
 arch/mips/kernel/cpu-probe.c         | 13 +++++++++++++
 arch/mips/kernel/traps.c             |  3 ++-
 4 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/cpu-features.h b/arch/mips/include/asm/cpu-features.h
index 724dfddcab92..0b1bc7ed913b 100644
--- a/arch/mips/include/asm/cpu-features.h
+++ b/arch/mips/include/asm/cpu-features.h
@@ -568,6 +568,10 @@
 # define cpu_has_mac2008_only	__opt(MIPS_CPU_MAC_2008_ONLY)
 #endif
 
+#ifndef cpu_has_ftlbparex
+# define cpu_has_ftlbparex	__opt(MIPS_CPU_FTLBPAREX)
+#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 104a509312b3..3a4773714b29 100644
--- a/arch/mips/include/asm/cpu.h
+++ b/arch/mips/include/asm/cpu.h
@@ -425,6 +425,7 @@ enum cpu_type_enum {
 #define MIPS_CPU_MM_SYSAD	BIT_ULL(58)	/* CPU supports write-through SysAD Valid merge */
 #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 */
 
 /*
  * CPU ASE encodings
diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index c231c1b67889..9e325862e810 100644
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -1827,6 +1827,19 @@ static inline void cpu_probe_mips(struct cpuinfo_mips *c, unsigned int cpu)
 	default:
 		break;
 	}
+
+	/* Recent MIPS cores use the implementation-dependent ExcCode 16 for
+	 * cache/FTLB parity exceptions.
+	 */
+	switch (__get_cpu_type(c->cputype)) {
+	case CPU_PROAPTIV:
+	case CPU_P5600:
+	case CPU_P6600:
+	case CPU_I6400:
+	case CPU_I6500:
+		c->options |= MIPS_CPU_FTLBPAREX;
+		break;
+	}
 }
 
 static inline void cpu_probe_alchemy(struct cpuinfo_mips *c, unsigned int cpu)
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 7c32c956156a..25a8a0d441be 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -2454,7 +2454,8 @@ void __init trap_init(void)
 	if (cpu_has_fpu && !cpu_has_nofpuex)
 		set_except_vector(EXCCODE_FPE, handle_fpe);
 
-	set_except_vector(MIPS_EXCCODE_TLBPAR, handle_ftlb);
+	if (cpu_has_ftlbparex)
+		set_except_vector(MIPS_EXCCODE_TLBPAR, handle_ftlb);
 
 	if (cpu_has_rixiex) {
 		set_except_vector(EXCCODE_TLBRI, tlb_do_page_fault_0);
-- 
2.25.1


^ permalink raw reply	[flat|nested] 6+ messages in thread

* [PATCH v3 2/3] MIPS: add definitions for Loongson-specific CP0.Diag1 register
  2020-07-27 16:51 [PATCH v3 0/3] Refactor FTLBPar exception handling and add GSExc handler WANG Xuerui
  2020-07-27 16:51 ` [PATCH v3 1/3] MIPS: only register FTLBPar exception handler for supported models WANG Xuerui
@ 2020-07-27 16:51 ` WANG Xuerui
  2020-07-27 16:51 ` [PATCH v3 3/3] MIPS: handle Loongson-specific GSExc exception WANG Xuerui
  2020-07-28  5:47 ` [PATCH v3 0/3] Refactor FTLBPar exception handling and add GSExc handler Huacai Chen
  3 siblings, 0 replies; 6+ messages in thread
From: WANG Xuerui @ 2020-07-27 16:51 UTC (permalink / raw)
  To: linux-mips; +Cc: WANG Xuerui, Huacai Chen, Jiaxun Yang, Tiezhu Yang

This register is named GSCause in Loongson manuals. It carries Loongson
extended exception information.

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/mipsregs.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h
index 11094d857b92..5ba268266d16 100644
--- a/arch/mips/include/asm/mipsregs.h
+++ b/arch/mips/include/asm/mipsregs.h
@@ -86,6 +86,7 @@
 #define CP0_XCONTEXT $20
 #define CP0_FRAMEMASK $21
 #define CP0_DIAGNOSTIC $22
+#define CP0_DIAGNOSTIC1 $22, 1
 #define CP0_DEBUG $23
 #define CP0_DEPC $24
 #define CP0_PERFORMANCE $25
@@ -1051,6 +1052,13 @@
 /* Flush FTLB */
 #define LOONGSON_DIAG_FTLB	(_ULCAST_(1) << 13)
 
+/*
+ * Diag1 (GSCause in Loongson-speak) fields
+ */
+/* Loongson-specific exception code (GSExcCode) */
+#define LOONGSON_DIAG1_EXCCODE_SHIFT	2
+#define LOONGSON_DIAG1_EXCCODE		GENMASK(6, 2)
+
 /* CvmCtl register field definitions */
 #define CVMCTL_IPPCI_SHIFT	7
 #define CVMCTL_IPPCI		(_U64CAST_(0x7) << CVMCTL_IPPCI_SHIFT)
-- 
2.25.1


^ permalink raw reply	[flat|nested] 6+ messages in thread

* [PATCH v3 3/3] MIPS: handle Loongson-specific GSExc exception
  2020-07-27 16:51 [PATCH v3 0/3] Refactor FTLBPar exception handling and add GSExc handler WANG Xuerui
  2020-07-27 16:51 ` [PATCH v3 1/3] MIPS: only register FTLBPar exception handler for supported models WANG Xuerui
  2020-07-27 16:51 ` [PATCH v3 2/3] MIPS: add definitions for Loongson-specific CP0.Diag1 register WANG Xuerui
@ 2020-07-27 16:51 ` WANG Xuerui
  2020-07-28  7:40   ` WANG Xuerui
  2020-07-28  5:47 ` [PATCH v3 0/3] Refactor FTLBPar exception handling and add GSExc handler Huacai Chen
  3 siblings, 1 reply; 6+ messages in thread
From: WANG Xuerui @ 2020-07-27 16:51 UTC (permalink / raw)
  To: linux-mips; +Cc: WANG Xuerui, Huacai Chen, Jiaxun Yang, Tiezhu Yang

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
+	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);
-- 
2.25.1


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH v3 0/3] Refactor FTLBPar exception handling and add GSExc handler
  2020-07-27 16:51 [PATCH v3 0/3] Refactor FTLBPar exception handling and add GSExc handler WANG Xuerui
                   ` (2 preceding siblings ...)
  2020-07-27 16:51 ` [PATCH v3 3/3] MIPS: handle Loongson-specific GSExc exception WANG Xuerui
@ 2020-07-28  5:47 ` Huacai Chen
  3 siblings, 0 replies; 6+ messages in thread
From: Huacai Chen @ 2020-07-28  5:47 UTC (permalink / raw)
  To: WANG Xuerui; +Cc: open list:MIPS

For the whole series:

Reviewed-by: Huacai Chen <chenhc@lemote.com>

On Tue, Jul 28, 2020 at 2:53 AM WANG Xuerui <git@xen0n.name> wrote:
>
> It was found that some undocumented unprivileged instructions could
> crash the kernel with a "FTLB parity error" on Loongson-3A4000, but the
> error registers were garbage:
>
> [  896.970419] FTLB error exception, cp0_ecc=0x00000002:
> [  896.975446] cp0_errorepc == ffffffffffffffff
> [  896.979755] c0_cacheerr == 00000000
> [  896.983277] Decoded c0_cacheerr: primary cache fault in insn reference.
> [  896.989963] Cache error exception:
> [  896.993396] cp0_errorepc == ffffffffffffffff
> [  896.997707] c0_cacheerr == 00000000
> [  897.001228] Decoded c0_cacheerr: primary cache fault in insn reference.
> [  897.007916] Error bits:
> [  897.010467] IDX: 0x00000000
> [  897.013284] Kernel panic - not syncing: Can't handle the cache error!
> [  897.019807] ---[ end Kernel panic - not syncing: Can't handle the cache error! ]---
>
> Turns out the FTLBPar exception code is actually implementation-specific.
> On Loongson cores the exception is "GSExc" instead, and is non-fatal in
> Loongson's linux-3.10 fork. So we dynamically register the correct handler
> for the exception, and do not panic on the specific undocumented case.
>
> P.S. There is not much space left in the cpuinfo_mips.options flag. We
> should consider moving to something like x86's feature flags that is
> extensible.
>
> v3:
> - Simplified declaration of cpu_has_gsexcex, as suggested by Huacai
>
> v2:
> - Removed stray GSExc logic in cpu_probe_legacy, pointed out by Huacai
>
> WANG Xuerui (3):
>   MIPS: only register FTLBPar exception handler for supported models
>   MIPS: add definitions for Loongson-specific CP0.Diag1 register
>   MIPS: handle Loongson-specific GSExc exception
>
>  arch/mips/include/asm/cpu-features.h |  8 ++++++
>  arch/mips/include/asm/cpu.h          |  2 ++
>  arch/mips/include/asm/mipsregs.h     | 11 ++++++++
>  arch/mips/kernel/cpu-probe.c         | 16 ++++++++++++
>  arch/mips/kernel/genex.S             |  7 +++++
>  arch/mips/kernel/traps.c             | 38 +++++++++++++++++++++++++++-
>  6 files changed, 81 insertions(+), 1 deletion(-)
>
> --
> 2.25.1
>

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH v3 3/3] MIPS: handle Loongson-specific GSExc exception
  2020-07-27 16:51 ` [PATCH v3 3/3] MIPS: handle Loongson-specific GSExc exception WANG Xuerui
@ 2020-07-28  7:40   ` WANG Xuerui
  0 siblings, 0 replies; 6+ messages in thread
From: WANG Xuerui @ 2020-07-28  7:40 UTC (permalink / raw)
  To: WANG Xuerui, linux-mips; +Cc: Huacai Chen, Jiaxun Yang, Tiezhu Yang

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);

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, back to index

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-07-27 16:51 [PATCH v3 0/3] Refactor FTLBPar exception handling and add GSExc handler WANG Xuerui
2020-07-27 16:51 ` [PATCH v3 1/3] MIPS: only register FTLBPar exception handler for supported models WANG Xuerui
2020-07-27 16:51 ` [PATCH v3 2/3] MIPS: add definitions for Loongson-specific CP0.Diag1 register WANG Xuerui
2020-07-27 16:51 ` [PATCH v3 3/3] MIPS: handle Loongson-specific GSExc exception WANG Xuerui
2020-07-28  7:40   ` WANG Xuerui
2020-07-28  5:47 ` [PATCH v3 0/3] Refactor FTLBPar exception handling and add GSExc handler Huacai Chen

Linux-MIPS Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mips/0 linux-mips/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mips linux-mips/ https://lore.kernel.org/linux-mips \
		linux-mips@vger.kernel.org
	public-inbox-index linux-mips

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-mips


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git