[PATCH 2/4] ftrace: Check against is_kernel_text() instead of kaslr_offset()

[Steven Rostedt]

From: Steven Rostedt <rostedt at goodmis.org>

As kaslr_offset() is architecture dependent and also may not be defined by
all architectures, when zeroing out unused weak functions, do not check
against kaslr_offset(), but instead check if the address is within the
kernel text sections. If KASLR added a shift to the zeroed out function,
it would still not be located in the kernel text. This is a more robust
way to test if the text is valid or not.

Fixes: ef378c3b8233 ("scripts/sorttable: Zero out weak functions in mcount_loc table")
Reported-by: Nathan Chancellor <nathan at kernel.org>
Reported-by: Mark Brown <broonie at kernel.org>
Tested-by: Nathan Chancellor <nathan at kernel.org>
Closes: https://lore.kernel.org/all/20250224180805.GA1536711@ax162/
Closes: https://lore.kernel.org/all/5225b07b-a9b2-4558-9d5f-aa60b19f6317@sirena.org.uk/
Signed-off-by: Steven Rostedt (Google) <rostedt at goodmis.org>
---
 kernel/trace/ftrace.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 183f72cf15ed..bec7b5dbdb3b 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7004,7 +7004,6 @@ static int ftrace_process_locs(struct module *mod,
 	unsigned long count;
 	unsigned long *p;
 	unsigned long addr;
-	unsigned long kaslr;
 	unsigned long flags = 0; /* Shut up gcc */
 	unsigned long pages;
 	int ret = -ENOMEM;
@@ -7056,9 +7055,6 @@ static int ftrace_process_locs(struct module *mod,
 		ftrace_pages->next = start_pg;
 	}
 
-	/* For zeroed locations that were shifted for core kernel */
-	kaslr = !mod ? kaslr_offset() : 0;
-
 	p = start;
 	pg = start_pg;
 	while (p < end) {
@@ -7072,7 +7068,18 @@ static int ftrace_process_locs(struct module *mod,
 		 * object files to satisfy alignments.
 		 * Skip any NULL pointers.
 		 */
-		if (!addr || addr == kaslr) {
+		if (!addr) {
+			skipped++;
+			continue;
+		}
+
+		/*
+		 * If this is core kernel, make sure the address is in core
+		 * or inittext, as weak functions get zeroed and KASLR can
+		 * move them to something other than zero. It just will not
+		 * move it to an area where kernel text is.
+		 */
+		if (!mod && !(is_kernel_text(addr) || is_kernel_inittext(addr))) {
 			skipped++;
 			continue;
 		}
-- 
2.47.2