[PATCH v3] RISC-V: Check clint_time_val before use

[PATCH v3] RISC-V: Check clint_time_val before use

[Anup Patel]

The NoMMU kernel is broken for QEMU virt machine from Linux-5.9-rc6
because clint_time_val is used even before CLINT driver is probed
at following places:
1. rand_initialize() calls get_cycles() which in-turn uses
   clint_time_val
2. boot_init_stack_canary() calls get_cycles() which in-turn
   uses clint_time_val

The issue#1 (above) is fixed by providing custom random_get_entropy()
for RISC-V NoMMU kernel. For issue#2 (above), we remove dependency of
boot_init_stack_canary() on get_cycles() and this is aligned with the
boot_init_stack_canary() implementations of ARM, ARM64 and MIPS kernel.

Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
for M-mode systems")
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>
---
Changes since v2:
 - Take different approach and provide custom random_get_entropy() for
   RISC-V NoMMU kernel
 - Remove dependency of boot_init_stack_canary() on get_cycles()
 - Hopefully we don't require to set clint_time_val = NULL in CLINT
   driver with a different approach to fix.
Changes since v1:
 - Explicitly initialize clint_time_val to NULL in CLINT driver to
   avoid hang on Kendryte K210
---
 arch/riscv/include/asm/stackprotector.h |  4 ----
 arch/riscv/include/asm/timex.h          | 13 +++++++++++++
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/stackprotector.h b/arch/riscv/include/asm/stackprotector.h
index d95f7b2a7f37..5962f8891f06 100644
--- a/arch/riscv/include/asm/stackprotector.h
+++ b/arch/riscv/include/asm/stackprotector.h
@@ -5,7 +5,6 @@
 
 #include <linux/random.h>
 #include <linux/version.h>
-#include <asm/timex.h>
 
 extern unsigned long __stack_chk_guard;
 
@@ -18,12 +17,9 @@ extern unsigned long __stack_chk_guard;
 static __always_inline void boot_init_stack_canary(void)
 {
 	unsigned long canary;
-	unsigned long tsc;
 
 	/* Try to get a semi random initial value. */
 	get_random_bytes(&canary, sizeof(canary));
-	tsc = get_cycles();
-	canary += tsc + (tsc << BITS_PER_LONG/2);
 	canary ^= LINUX_VERSION_CODE;
 	canary &= CANARY_MASK;
 
diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
index 7f659dda0032..ab104905d4db 100644
--- a/arch/riscv/include/asm/timex.h
+++ b/arch/riscv/include/asm/timex.h
@@ -33,6 +33,19 @@ static inline u32 get_cycles_hi(void)
 #define get_cycles_hi get_cycles_hi
 #endif /* CONFIG_64BIT */
 
+/*
+ * Much like MIPS, we may not have a viable counter to use at an early point
+ * in the boot process. Unfortunately we don't have a fallback, so instead
+ * we just return 0.
+ */
+static inline unsigned long random_get_entropy(void)
+{
+	if (unlikely(clint_time_val == NULL))
+		return 0;
+	return get_cycles();
+}
+#define random_get_entropy()	random_get_entropy()
+
 #else /* CONFIG_RISCV_M_MODE */
 
 static inline cycles_t get_cycles(void)
-- 
2.25.1


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Re: [PATCH v3] RISC-V: Check clint_time_val before use

[Palmer Dabbelt]

On Sat, 26 Sep 2020 22:39:16 PDT (-0700), Anup Patel wrote:
> The NoMMU kernel is broken for QEMU virt machine from Linux-5.9-rc6
> because clint_time_val is used even before CLINT driver is probed
> at following places:
> 1. rand_initialize() calls get_cycles() which in-turn uses
>    clint_time_val
> 2. boot_init_stack_canary() calls get_cycles() which in-turn
>    uses clint_time_val
>
> The issue#1 (above) is fixed by providing custom random_get_entropy()
> for RISC-V NoMMU kernel. For issue#2 (above), we remove dependency of
> boot_init_stack_canary() on get_cycles() and this is aligned with the
> boot_init_stack_canary() implementations of ARM, ARM64 and MIPS kernel.
>
> Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
> for M-mode systems")
> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
> Signed-off-by: Anup Patel <anup.patel@wdc.com>
> ---
> Changes since v2:
>  - Take different approach and provide custom random_get_entropy() for
>    RISC-V NoMMU kernel
>  - Remove dependency of boot_init_stack_canary() on get_cycles()
>  - Hopefully we don't require to set clint_time_val = NULL in CLINT
>    driver with a different approach to fix.
> Changes since v1:
>  - Explicitly initialize clint_time_val to NULL in CLINT driver to
>    avoid hang on Kendryte K210
> ---
>  arch/riscv/include/asm/stackprotector.h |  4 ----
>  arch/riscv/include/asm/timex.h          | 13 +++++++++++++
>  2 files changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/include/asm/stackprotector.h b/arch/riscv/include/asm/stackprotector.h
> index d95f7b2a7f37..5962f8891f06 100644
> --- a/arch/riscv/include/asm/stackprotector.h
> +++ b/arch/riscv/include/asm/stackprotector.h
> @@ -5,7 +5,6 @@
>
>  #include <linux/random.h>
>  #include <linux/version.h>
> -#include <asm/timex.h>
>
>  extern unsigned long __stack_chk_guard;
>
> @@ -18,12 +17,9 @@ extern unsigned long __stack_chk_guard;
>  static __always_inline void boot_init_stack_canary(void)
>  {
>  	unsigned long canary;
> -	unsigned long tsc;
>
>  	/* Try to get a semi random initial value. */
>  	get_random_bytes(&canary, sizeof(canary));
> -	tsc = get_cycles();
> -	canary += tsc + (tsc << BITS_PER_LONG/2);
>  	canary ^= LINUX_VERSION_CODE;
>  	canary &= CANARY_MASK;
>
> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
> index 7f659dda0032..ab104905d4db 100644
> --- a/arch/riscv/include/asm/timex.h
> +++ b/arch/riscv/include/asm/timex.h
> @@ -33,6 +33,19 @@ static inline u32 get_cycles_hi(void)
>  #define get_cycles_hi get_cycles_hi
>  #endif /* CONFIG_64BIT */
>
> +/*
> + * Much like MIPS, we may not have a viable counter to use at an early point
> + * in the boot process. Unfortunately we don't have a fallback, so instead
> + * we just return 0.
> + */
> +static inline unsigned long random_get_entropy(void)
> +{
> +	if (unlikely(clint_time_val == NULL))
> +		return 0;
> +	return get_cycles();
> +}
> +#define random_get_entropy()	random_get_entropy()
> +
>  #else /* CONFIG_RISCV_M_MODE */
>
>  static inline cycles_t get_cycles(void)

Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>

I'm going to wait for Damien to chime in about the NULL initialization boot
failure, though, as I'm a bit worried something else was going on.

Thanks!

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Re: [PATCH v3] RISC-V: Check clint_time_val before use

[Damien Le Moal]

On Sat, 2020-09-26 at 22:46 -0700, Palmer Dabbelt wrote:
> On Sat, 26 Sep 2020 22:39:16 PDT (-0700), Anup Patel wrote:
> > The NoMMU kernel is broken for QEMU virt machine from Linux-5.9-rc6
> > because clint_time_val is used even before CLINT driver is probed
> > at following places:
> > 1. rand_initialize() calls get_cycles() which in-turn uses
> >    clint_time_val
> > 2. boot_init_stack_canary() calls get_cycles() which in-turn
> >    uses clint_time_val
> > 
> > The issue#1 (above) is fixed by providing custom random_get_entropy()
> > for RISC-V NoMMU kernel. For issue#2 (above), we remove dependency of
> > boot_init_stack_canary() on get_cycles() and this is aligned with the
> > boot_init_stack_canary() implementations of ARM, ARM64 and MIPS kernel.
> > 
> > Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
> > for M-mode systems")
> > Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
> > Signed-off-by: Anup Patel <anup.patel@wdc.com>
> > ---
> > Changes since v2:
> >  - Take different approach and provide custom random_get_entropy() for
> >    RISC-V NoMMU kernel
> >  - Remove dependency of boot_init_stack_canary() on get_cycles()
> >  - Hopefully we don't require to set clint_time_val = NULL in CLINT
> >    driver with a different approach to fix.
> > Changes since v1:
> >  - Explicitly initialize clint_time_val to NULL in CLINT driver to
> >    avoid hang on Kendryte K210
> > ---
> >  arch/riscv/include/asm/stackprotector.h |  4 ----
> >  arch/riscv/include/asm/timex.h          | 13 +++++++++++++
> >  2 files changed, 13 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/riscv/include/asm/stackprotector.h b/arch/riscv/include/asm/stackprotector.h
> > index d95f7b2a7f37..5962f8891f06 100644
> > --- a/arch/riscv/include/asm/stackprotector.h
> > +++ b/arch/riscv/include/asm/stackprotector.h
> > @@ -5,7 +5,6 @@
> > 
> >  #include <linux/random.h>
> >  #include <linux/version.h>
> > -#include <asm/timex.h>
> > 
> >  extern unsigned long __stack_chk_guard;
> > 
> > @@ -18,12 +17,9 @@ extern unsigned long __stack_chk_guard;
> >  static __always_inline void boot_init_stack_canary(void)
> >  {
> >  	unsigned long canary;
> > -	unsigned long tsc;
> > 
> >  	/* Try to get a semi random initial value. */
> >  	get_random_bytes(&canary, sizeof(canary));
> > -	tsc = get_cycles();
> > -	canary += tsc + (tsc << BITS_PER_LONG/2);
> >  	canary ^= LINUX_VERSION_CODE;
> >  	canary &= CANARY_MASK;
> > 
> > diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
> > index 7f659dda0032..ab104905d4db 100644
> > --- a/arch/riscv/include/asm/timex.h
> > +++ b/arch/riscv/include/asm/timex.h
> > @@ -33,6 +33,19 @@ static inline u32 get_cycles_hi(void)
> >  #define get_cycles_hi get_cycles_hi
> >  #endif /* CONFIG_64BIT */
> > 
> > +/*
> > + * Much like MIPS, we may not have a viable counter to use at an early point
> > + * in the boot process. Unfortunately we don't have a fallback, so instead
> > + * we just return 0.
> > + */
> > +static inline unsigned long random_get_entropy(void)
> > +{
> > +	if (unlikely(clint_time_val == NULL))
> > +		return 0;
> > +	return get_cycles();
> > +}
> > +#define random_get_entropy()	random_get_entropy()
> > +
> >  #else /* CONFIG_RISCV_M_MODE */
> > 
> >  static inline cycles_t get_cycles(void)
> 
> Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
> 
> I'm going to wait for Damien to chime in about the NULL initialization boot
> failure, though, as I'm a bit worried something else was going on.
> 
> Thanks!

For Kendryte, no problems. Boots correctly.

Tested-by: Damien Le Moal <damien.lemoal@wdc.com>



-- 
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Western Digital
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Re: [PATCH v3] RISC-V: Check clint_time_val before use

[Damien Le Moal]

On Sun, 2020-09-27 at 11:09 +0530, Anup Patel wrote:
> The NoMMU kernel is broken for QEMU virt machine from Linux-5.9-rc6
> because clint_time_val is used even before CLINT driver is probed
> at following places:
> 1. rand_initialize() calls get_cycles() which in-turn uses
>    clint_time_val
> 2. boot_init_stack_canary() calls get_cycles() which in-turn
>    uses clint_time_val
> 
> The issue#1 (above) is fixed by providing custom random_get_entropy()
> for RISC-V NoMMU kernel. For issue#2 (above), we remove dependency of
> boot_init_stack_canary() on get_cycles() and this is aligned with the
> boot_init_stack_canary() implementations of ARM, ARM64 and MIPS kernel.
> 
> Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
> for M-mode systems")
> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
> Signed-off-by: Anup Patel <anup.patel@wdc.com>
> ---
> Changes since v2:
>  - Take different approach and provide custom random_get_entropy() for
>    RISC-V NoMMU kernel
>  - Remove dependency of boot_init_stack_canary() on get_cycles()
>  - Hopefully we don't require to set clint_time_val = NULL in CLINT
>    driver with a different approach to fix.
> Changes since v1:
>  - Explicitly initialize clint_time_val to NULL in CLINT driver to
>    avoid hang on Kendryte K210
> ---
>  arch/riscv/include/asm/stackprotector.h |  4 ----
>  arch/riscv/include/asm/timex.h          | 13 +++++++++++++
>  2 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/stackprotector.h b/arch/riscv/include/asm/stackprotector.h
> index d95f7b2a7f37..5962f8891f06 100644
> --- a/arch/riscv/include/asm/stackprotector.h
> +++ b/arch/riscv/include/asm/stackprotector.h
> @@ -5,7 +5,6 @@
>  
>  #include <linux/random.h>
>  #include <linux/version.h>
> -#include <asm/timex.h>
>  
>  extern unsigned long __stack_chk_guard;
>  
> @@ -18,12 +17,9 @@ extern unsigned long __stack_chk_guard;
>  static __always_inline void boot_init_stack_canary(void)
>  {
>  	unsigned long canary;
> -	unsigned long tsc;
>  
>  	/* Try to get a semi random initial value. */
>  	get_random_bytes(&canary, sizeof(canary));
> -	tsc = get_cycles();
> -	canary += tsc + (tsc << BITS_PER_LONG/2);
>  	canary ^= LINUX_VERSION_CODE;
>  	canary &= CANARY_MASK;
>  
> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
> index 7f659dda0032..ab104905d4db 100644
> --- a/arch/riscv/include/asm/timex.h
> +++ b/arch/riscv/include/asm/timex.h
> @@ -33,6 +33,19 @@ static inline u32 get_cycles_hi(void)
>  #define get_cycles_hi get_cycles_hi
>  #endif /* CONFIG_64BIT */
>  
> +/*
> + * Much like MIPS, we may not have a viable counter to use at an early point
> + * in the boot process. Unfortunately we don't have a fallback, so instead
> + * we just return 0.
> + */
> +static inline unsigned long random_get_entropy(void)
> +{
> +	if (unlikely(clint_time_val == NULL))
> +		return 0;
> +	return get_cycles();
> +}
> +#define random_get_entropy()	random_get_entropy()
> +
>  #else /* CONFIG_RISCV_M_MODE */
>  
>  static inline cycles_t get_cycles(void)

Did not reply to the patch... So again for Kendryte:

Tested-by: Damien Le Moal <damien.lemoal@wdc.com>


-- 
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Western Digital
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Re: [PATCH v3] RISC-V: Check clint_time_val before use

[Palmer Dabbelt]

On Sat, 26 Sep 2020 22:52:19 PDT (-0700), Damien Le Moal wrote:
> On Sun, 2020-09-27 at 11:09 +0530, Anup Patel wrote:
>> The NoMMU kernel is broken for QEMU virt machine from Linux-5.9-rc6
>> because clint_time_val is used even before CLINT driver is probed
>> at following places:
>> 1. rand_initialize() calls get_cycles() which in-turn uses
>>    clint_time_val
>> 2. boot_init_stack_canary() calls get_cycles() which in-turn
>>    uses clint_time_val
>> 
>> The issue#1 (above) is fixed by providing custom random_get_entropy()
>> for RISC-V NoMMU kernel. For issue#2 (above), we remove dependency of
>> boot_init_stack_canary() on get_cycles() and this is aligned with the
>> boot_init_stack_canary() implementations of ARM, ARM64 and MIPS kernel.
>> 
>> Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
>> for M-mode systems")
>> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
>> Signed-off-by: Anup Patel <anup.patel@wdc.com>
>> ---
>> Changes since v2:
>>  - Take different approach and provide custom random_get_entropy() for
>>    RISC-V NoMMU kernel
>>  - Remove dependency of boot_init_stack_canary() on get_cycles()
>>  - Hopefully we don't require to set clint_time_val = NULL in CLINT
>>    driver with a different approach to fix.
>> Changes since v1:
>>  - Explicitly initialize clint_time_val to NULL in CLINT driver to
>>    avoid hang on Kendryte K210
>> ---
>>  arch/riscv/include/asm/stackprotector.h |  4 ----
>>  arch/riscv/include/asm/timex.h          | 13 +++++++++++++
>>  2 files changed, 13 insertions(+), 4 deletions(-)
>> 
>> diff --git a/arch/riscv/include/asm/stackprotector.h b/arch/riscv/include/asm/stackprotector.h
>> index d95f7b2a7f37..5962f8891f06 100644
>> --- a/arch/riscv/include/asm/stackprotector.h
>> +++ b/arch/riscv/include/asm/stackprotector.h
>> @@ -5,7 +5,6 @@
>>  
>>  #include <linux/random.h>
>>  #include <linux/version.h>
>> -#include <asm/timex.h>
>>  
>>  extern unsigned long __stack_chk_guard;
>>  
>> @@ -18,12 +17,9 @@ extern unsigned long __stack_chk_guard;
>>  static __always_inline void boot_init_stack_canary(void)
>>  {
>>  	unsigned long canary;
>> -	unsigned long tsc;
>>  
>>  	/* Try to get a semi random initial value. */
>>  	get_random_bytes(&canary, sizeof(canary));
>> -	tsc = get_cycles();
>> -	canary += tsc + (tsc << BITS_PER_LONG/2);
>>  	canary ^= LINUX_VERSION_CODE;
>>  	canary &= CANARY_MASK;
>>  
>> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
>> index 7f659dda0032..ab104905d4db 100644
>> --- a/arch/riscv/include/asm/timex.h
>> +++ b/arch/riscv/include/asm/timex.h
>> @@ -33,6 +33,19 @@ static inline u32 get_cycles_hi(void)
>>  #define get_cycles_hi get_cycles_hi
>>  #endif /* CONFIG_64BIT */
>>  
>> +/*
>> + * Much like MIPS, we may not have a viable counter to use at an early point
>> + * in the boot process. Unfortunately we don't have a fallback, so instead
>> + * we just return 0.
>> + */
>> +static inline unsigned long random_get_entropy(void)
>> +{
>> +	if (unlikely(clint_time_val == NULL))
>> +		return 0;
>> +	return get_cycles();
>> +}
>> +#define random_get_entropy()	random_get_entropy()
>> +
>>  #else /* CONFIG_RISCV_M_MODE */
>>  
>>  static inline cycles_t get_cycles(void)
> 
> Did not reply to the patch... So again for Kendryte:
> 
> Tested-by: Damien Le Moal <damien.lemoal@wdc.com>

Thanks.  I've put this on for-next, right after the patch I just posted to add
EXPORT_SYMBOL(clint_time_val) as it turns out random_get_entropy() is used by a
driver.

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