Linux-RISC-V Archive on lore.kernel.org
 help / color / Atom feed
From: Palmer Dabbelt <palmerdabbelt@google.com>
To: Damien Le Moal <Damien.LeMoal@wdc.com>
Cc: aou@eecs.berkeley.edu, anup@brainfault.org,
	Anup Patel <Anup.Patel@wdc.com>,
	linux-kernel@vger.kernel.org, Atish Patra <Atish.Patra@wdc.com>,
	Alistair Francis <Alistair.Francis@wdc.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	linux-riscv@lists.infradead.org
Subject: Re: [PATCH v3] RISC-V: Check clint_time_val before use
Date: Tue, 29 Sep 2020 23:58:27 -0700 (PDT)
Message-ID: <mhng-6eec6bf8-1c59-4c5a-9a93-8e4f7bd7faed@palmerdabbelt-glaptop1> (raw)
In-Reply-To: <c0ec481bf0413f391b16415530d2606114ea150a.camel@wdc.com>

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.

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

      reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-27  5:39 Anup Patel
2020-09-27  5:46 ` Palmer Dabbelt
2020-09-27  5:51   ` Damien Le Moal
2020-09-27  5:52 ` Damien Le Moal
2020-09-30  6:58   ` Palmer Dabbelt [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=mhng-6eec6bf8-1c59-4c5a-9a93-8e4f7bd7faed@palmerdabbelt-glaptop1 \
    --to=palmerdabbelt@google.com \
    --cc=Alistair.Francis@wdc.com \
    --cc=Anup.Patel@wdc.com \
    --cc=Atish.Patra@wdc.com \
    --cc=Damien.LeMoal@wdc.com \
    --cc=anup@brainfault.org \
    --cc=aou@eecs.berkeley.edu \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-riscv@lists.infradead.org \
    --cc=paul.walmsley@sifive.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-RISC-V Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-riscv/0 linux-riscv/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-riscv linux-riscv/ https://lore.kernel.org/linux-riscv \
		linux-riscv@lists.infradead.org
	public-inbox-index linux-riscv

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.infradead.lists.linux-riscv


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