[PATCH v4] lib: sbi: pmu: Return SBI_EINVAL if cidx_mask is 0

[James Raphael Tiovalen]

Currently, when configuring a matching programmable HPM counter with
Sscofpmf being present, cidx_base > 2, and cidx_mask == 0 to monitor
either the CPU_CYCLES or INSTRUCTIONS hardware event,
sbi_pmu_ctr_cfg_match will succeed but it will configure the
corresponding fixed counter instead of the counter specified by the
cidx_base parameter.

During counter configuration, the following issues may arise:
- If the SKIP_MATCH flag is set, an out-of-bounds memory read of the
phs->active_events array would occur, which could lead to undefined
behavior.

- If the CLEAR_VALUE flag is set, the corresponding fixed counter will
be reset, which could be considered unexpected behavior.

- If the AUTO_START flag is set, pmu_ctr_start_hw will silently start
the fixed counter, even though it has already started. From the
supervisor's perspective, nothing has changed, which could be confusing.
The supervisor will not see the SBI_ERR_ALREADY_STARTED error code since
sbi_pmu_ctr_cfg_match does not return the error code of
pmu_ctr_start_hw.

The only way to detect these issues is to check the ctr_idx return value
of sbi_pmu_ctr_cfg_match and compare it with cidx_base.

Fix these issues by returning the SBI_ERR_INVALID_PARAM error code if
the cidx_mask parameter value being passed in is 0 since an invalid
parameter should not lead to a successful sbi_pmu_ctr_cfg_match but with
unexpected side effects.

Following a similar rationale, add the validation check to
sbi_pmu_ctr_start and sbi_pmu_ctr_stop as well since sbi_fls is
undefined when the mask is 0.

This also aligns OpenSBI's behavior with KVM's.

Signed-off-by: James Raphael Tiovalen <jamestiotio at gmail.com>
Reviewed-by: Atish Patra <atishp at rivosinc.com>
Reviewed-by: Andrew Jones <ajones at ventanamicro.com>
---
 lib/sbi/sbi_pmu.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/lib/sbi/sbi_pmu.c b/lib/sbi/sbi_pmu.c
index 5983a78..6ca4efd 100644
--- a/lib/sbi/sbi_pmu.c
+++ b/lib/sbi/sbi_pmu.c
@@ -206,6 +206,12 @@ static int pmu_ctr_validate(struct sbi_pmu_hart_state *phs,
 	return event_idx_type;
 }
 
+static bool pmu_ctr_idx_validate(unsigned long cbase, unsigned long cmask)
+{
+	/* Do a basic sanity check of counter base & mask */
+	return cmask && cbase + sbi_fls(cmask) < total_ctrs;
+}
+
 int sbi_pmu_ctr_fw_read(uint32_t cidx, uint64_t *cval)
 {
 	int event_idx_type;
@@ -472,7 +478,7 @@ int sbi_pmu_ctr_start(unsigned long cbase, unsigned long cmask,
 	int i, cidx;
 	uint64_t edata;
 
-	if ((cbase + sbi_fls(cmask)) >= total_ctrs)
+	if (!pmu_ctr_idx_validate(cbase, cmask))
 		return ret;
 
 	if (flags & SBI_PMU_STOP_FLAG_TAKE_SNAPSHOT)
@@ -577,8 +583,8 @@ int sbi_pmu_ctr_stop(unsigned long cbase, unsigned long cmask,
 	uint32_t event_code;
 	int i, cidx;
 
-	if ((cbase + sbi_fls(cmask)) >= total_ctrs)
-		return SBI_EINVAL;
+	if (!pmu_ctr_idx_validate(cbase, cmask))
+		return ret;
 
 	if (flag & SBI_PMU_STOP_FLAG_TAKE_SNAPSHOT)
 		return SBI_ENO_SHMEM;
@@ -839,8 +845,7 @@ int sbi_pmu_ctr_cfg_match(unsigned long cidx_base, unsigned long cidx_mask,
 	int ret, event_type, ctr_idx = SBI_ENOTSUPP;
 	u32 event_code;
 
-	/* Do a basic sanity check of counter base & mask */
-	if ((cidx_base + sbi_fls(cidx_mask)) >= total_ctrs)
+	if (!pmu_ctr_idx_validate(cidx_base, cidx_mask))
 		return SBI_EINVAL;
 
 	event_type = pmu_event_validate(phs, event_idx, event_data);
-- 
2.43.0