[PATCH 2/7] perf,x86: Fix possible Spectre-v1 for hw_perf_event

[Peter Zijlstra]

> arch/x86/events/core.c:319 set_ext_hw_attr() warn: potential spectre issue 'hw_cache_event_ids[cache_type]' (local cap)
> arch/x86/events/core.c:319 set_ext_hw_attr() warn: potential spectre issue 'hw_cache_event_ids' (local cap)
> arch/x86/events/core.c:328 set_ext_hw_attr() warn: potential spectre issue 'hw_cache_extra_regs[cache_type]' (local cap)
> arch/x86/events/core.c:328 set_ext_hw_attr() warn: potential spectre issue 'hw_cache_extra_regs' (local cap)

Userspace controls @config which contains 3 (byte) fields used for a 3
dimensional array deref.

Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
 arch/x86/events/core.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -304,17 +304,20 @@ set_ext_hw_attr(struct hw_perf_event *hw
 
 	config = attr->config;
 
-	cache_type = (config >>  0) & 0xff;
+	cache_type = (config >> 0) & 0xff;
 	if (cache_type >= PERF_COUNT_HW_CACHE_MAX)
 		return -EINVAL;
+	cache_type = array_index_nospec(cache_type, PERF_COUNT_HW_CACHE_MAX);
 
 	cache_op = (config >>  8) & 0xff;
 	if (cache_op >= PERF_COUNT_HW_CACHE_OP_MAX)
 		return -EINVAL;
+	cache_op = array_index_nospec(cache_op, PERF_COUNT_HW_CACHE_OP_MAX);
 
 	cache_result = (config >> 16) & 0xff;
 	if (cache_result >= PERF_COUNT_HW_CACHE_RESULT_MAX)
 		return -EINVAL;
+	cache_result = array_index_nospec(cache_result, PERF_COUNT_HW_CACHE_RESULT_MAX);
 
 	val = hw_cache_event_ids[cache_type][cache_op][cache_result];