Commit aa988760 authored by Anup Patel's avatar Anup Patel Committed by Palmer Dabbelt

RISC-V: Check clint_time_val before use

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: d5be89a8 ("RISC-V: Resurrect the MMIO timer implementation for M-mode systems")
Signed-off-by: default avatarAnup Patel <anup.patel@wdc.com>
Tested-by: default avatarDamien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: default avatarPalmer Dabbelt <palmerdabbelt@google.com>
parent c14decfc
...@@ -5,7 +5,6 @@ ...@@ -5,7 +5,6 @@
#include <linux/random.h> #include <linux/random.h>
#include <linux/version.h> #include <linux/version.h>
#include <asm/timex.h>
extern unsigned long __stack_chk_guard; extern unsigned long __stack_chk_guard;
...@@ -18,12 +17,9 @@ 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) static __always_inline void boot_init_stack_canary(void)
{ {
unsigned long canary; unsigned long canary;
unsigned long tsc;
/* Try to get a semi random initial value. */ /* Try to get a semi random initial value. */
get_random_bytes(&canary, sizeof(canary)); get_random_bytes(&canary, sizeof(canary));
tsc = get_cycles();
canary += tsc + (tsc << BITS_PER_LONG/2);
canary ^= LINUX_VERSION_CODE; canary ^= LINUX_VERSION_CODE;
canary &= CANARY_MASK; canary &= CANARY_MASK;
......
...@@ -33,6 +33,19 @@ static inline u32 get_cycles_hi(void) ...@@ -33,6 +33,19 @@ static inline u32 get_cycles_hi(void)
#define get_cycles_hi get_cycles_hi #define get_cycles_hi get_cycles_hi
#endif /* CONFIG_64BIT */ #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 */ #else /* CONFIG_RISCV_M_MODE */
static inline cycles_t get_cycles(void) static inline cycles_t get_cycles(void)
......
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