opal-prd: handle devtmpfs mounted with noexec

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@gentoo.org>
Reviewed-by: Vasant Hegde <hegdevasant@linux.vnet.ibm.com>
[oliver: whitespace fix, add a comment, reflow commit message]
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>

1 files changed, 34 insertions, 2 deletions

diff --git a/external/opal-prd/opal-prd.c b/external/opal-prd/opal-prd.c
index d74d803..12269e8 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 +983,45 @@ 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_READ | 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;
+	}
+
+	/*
+	 * FIXME: We shouldn't be mapping the memory as RWX, but HBRT appears to
+	 * require the ability to write into the image at runtime.
+	 */
+	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;