[PATCH] lib: sbi: Only enable TM bit in scounteren

[Atish Patra]

The S-mode should disable Cycle and instruction counter for user space
to avoid side channel attacks. The Linux kernel already does this so that
any random user space code shouldn't be able to monitor cycle/instruction
without higher privilege mode involvement.

Remove the CY/IR bits in scountern in OpenSBI.

Signed-off-by: Atish Patra <atishp at rivosinc.com>
---
To: anup Patel <anup at brainfault.org>
Cc: opensbi at lists.infradead.org
---
 lib/sbi/sbi_hart.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
index fc4925b57625..177f356b7b77 100644
--- a/lib/sbi/sbi_hart.c
+++ b/lib/sbi/sbi_hart.c
@@ -49,10 +49,10 @@ static void mstatus_init(struct sbi_scratch *scratch)
 
 	csr_write(CSR_MSTATUS, mstatus_val);
 
-	/* Disable user mode usage of all perf counters except default ones (CY, TM, IR) */
+	/* Disable user mode usage of all perf counters except TM */
 	if (misa_extension('S') &&
 	    sbi_hart_priv_version(scratch) >= SBI_HART_PRIV_VER_1_10)
-		csr_write(CSR_SCOUNTEREN, 7);
+		csr_write(CSR_SCOUNTEREN, 0x02);
 
 	/**
 	 * OpenSBI doesn't use any PMU counters in M-mode.

---
base-commit: 316daaf1c299c29ac46e52145f65521f48ec63b5
change-id: 20250512-fix_scounteren-8b7b682bb864
--
Regards,
Atish patra