[Skiboot] [PATCH] opal-prd: handle devtmpfs mounted with noexec

[Georgy Yakovlev]

On systems using recent versions of systemd
/dev (devtmpfs) is mounted with noexec option.
Such mount prevents mapping HBRT image code region as RWX from /dev.
This commit, as suggested in github PR linked below,
attempts to work around the situation by copying
HBRT image to anon mmaped memory region and
sets mprotect rwx on it, allowing opal-prd to sucessfully
execute the code region.

Having memory region set as RWX is not ideal for security,
but fixing that is a separate and hard to solve problem.
Original code also mmaped region as RWX, so this PR does not
make things worse at least.

Closes: https://github.com/open-power/skiboot/issues/258
Signed-off-by: Georgy Yakovlev <gyakovlev at gentoo.org>
---
 external/opal-prd/opal-prd.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/external/opal-prd/opal-prd.c b/external/opal-prd/opal-prd.c
index d74d8039..abf43a78 100644
--- a/external/opal-prd/opal-prd.c
+++ b/external/opal-prd/opal-prd.c
@@ -973,7 +973,9 @@ static int map_hbrt_file(struct opal_prd_ctx *ctx, const char *name)
 static int map_hbrt_physmem(struct opal_prd_ctx *ctx, const char *name)
 {
 	struct prd_range *range;
+	int rc;
 	void *buf;
+	void *ro_buf;
 
 	range = find_range(name, 0);
 	if (!range) {
@@ -981,15 +983,41 @@ static int map_hbrt_physmem(struct opal_prd_ctx *ctx, const char *name)
 		return -1;
 	}
 
-	buf = mmap(NULL, range->size, PROT_READ | PROT_WRITE | PROT_EXEC,
+	ro_buf = mmap(NULL, range->size, PROT_READ,
 			MAP_PRIVATE, ctx->fd, range->physaddr);
-	if (buf == MAP_FAILED) {
+	if (ro_buf == MAP_FAILED) {
 		pr_log(LOG_ERR, "IMAGE: mmap(range:%s, "
 				"phys:0x%016lx, size:0x%016lx) failed: %m",
 				name, range->physaddr, range->size);
 		return -1;
 	}
 
+	buf = mmap(NULL, range->size, PROT_WRITE,	
+			MAP_SHARED | MAP_ANONYMOUS, -1 , 0);
+	if (buf == MAP_FAILED) {
+		pr_log(LOG_ERR, "IMAGE: anon mmap(size:0x%016lx) failed: %m",
+				range->size);
+		return -1;
+	}
+
+	memcpy(buf, ro_buf, range->size);
+
+	rc = munmap(ro_buf, range->size);
+	if (rc < 0) {
+		pr_log(LOG_ERR, "IMAGE: munmap("
+				"phys:0x%016lx, size:0x%016lx) failed: %m",
+				range->physaddr, range->size);
+		return -1;
+	}
+
+	rc = mprotect(buf, range->size, PROT_READ | PROT_WRITE | PROT_EXEC);
+	if (rc < 0) {
+		pr_log(LOG_ERR, "IMAGE: mprotect(phys:%p, "
+			"size:0x%016lx, rwx) failed: %m",
+			buf, range->size);
+		return -1;
+	}
+
 	ctx->code_addr = buf;
 	ctx->code_size = range->size;
 	return 0;
-- 
2.28.0