[PATCH] perf test amd ibs: avoid using executable heap

[Ondrej Mosnacek]

Making [parts of] the heap executable is dangerous and is blocked by
SELinux on Fedora/RHEL even for an unconfined user. Replace the malloc()
+ mprotect() combo with just mmap(), creating a private anonymous rwx
mapping, which only requires the more commonly allowed "execmem"
permission under SELinux (things like JIT or regex compilation need it
as well). mmap() with MAP_ANONYMOUS will give us a zeroed mapping that
begins on a page boundary, so the result is equivalent to the original
code even without a memset() or the page-alignment dance.

Verified that the test still passes on a machine with an AMD CPU that
has the "ibs" CPU flag.

Fixes: 35db59fa8ea2 ("perf test amd ibs: Add sample period unit test")
Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
---
 tools/perf/arch/x86/tests/amd-ibs-period.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/tools/perf/arch/x86/tests/amd-ibs-period.c b/tools/perf/arch/x86/tests/amd-ibs-period.c
index 6a92b3a23ed7a..b2210b1aa09fb 100644
--- a/tools/perf/arch/x86/tests/amd-ibs-period.c
+++ b/tools/perf/arch/x86/tests/amd-ibs-period.c
@@ -46,7 +46,6 @@ static int dummy_workload_1(unsigned long count)
 {
 	int (*func)(void);
 	int ret = 0;
-	char *p;
 	char insn1[] = {
 		0xb8, 0x01, 0x00, 0x00, 0x00, /* mov 1,%eax */
 		0xc3, /* ret */
@@ -59,18 +58,11 @@ static int dummy_workload_1(unsigned long count)
 		0xcc, /* int 3 */
 	};
 
-	p = calloc(2, page_size);
-	if (!p) {
-		printf("malloc() failed. %m");
-		return 1;
-	}
-
-	func = (void *)((unsigned long)(p + page_size - 1) & ~(page_size - 1));
-
-	ret = mprotect(func, page_size, PROT_READ | PROT_WRITE | PROT_EXEC);
-	if (ret) {
-		printf("mprotect() failed. %m");
-		goto out;
+	func = mmap(NULL, page_size, PROT_READ | PROT_WRITE | PROT_EXEC,
+		    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (!func) {
+		pr_debug("mmap() failed. %m\n");
+		return -1;
 	}
 
 	if (count < 100000)
@@ -93,7 +85,7 @@ static int dummy_workload_1(unsigned long count)
 	}
 
 out:
-	free(p);
+	munmap(func, page_size);
 	return ret;
 }
 
-- 
2.54.0