linux-kernel - [PATCH] powerpc64/ftrace: fix module loading without patchable function entries

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Message-ID: <20250204231821.39140-1-ailiop@suse.com>
Date: Wed,  5 Feb 2025 00:18:21 +0100
From: Anthony Iliopoulos <ailiop@...e.com>
To: <linuxppc-dev@...ts.ozlabs.org>
Cc: <linux-kernel@...r.kernel.org>,
	Naveen N Rao <naveen@...nel.org>
Subject: [PATCH] powerpc64/ftrace: fix module loading without patchable function entries

get_stubs_size assumes that there must always be at least one patchable
function entry, which is not always the case (modules that export data
but no code), otherwise it returns -ENOEXEC and thus the section header
sh_size is set to that value. During module_memory_alloc() the size is
passed to execmem_alloc() after being page-aligned and thus set to zero
which will cause it to fail the allocation (and thus module loading) as
__vmalloc_node_range() checks for zero-sized allocs and returns null:

[  115.466896] module_64: cast_common: doesn't contain __patchable_function_entries.
[  115.469189] ------------[ cut here ]------------
[  115.469496] WARNING: CPU: 0 PID: 274 at mm/vmalloc.c:3778 __vmalloc_node_range_noprof+0x8b4/0x8f0
...
[  115.478574] ---[ end trace 0000000000000000 ]---
[  115.479545] execmem: unable to allocate memory

Fix this by removing the check completely, since it is anyway not
helpful to propagate this as an error upwards.

Fixes: eec37961a56a ("powerpc64/ftrace: Move ftrace sequence out of line")
Signed-off-by: Anthony Iliopoulos <ailiop@...e.com>
---
 arch/powerpc/kernel/module_64.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 34a5aec4908f..126bf3b06ab7 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -258,10 +258,6 @@ static unsigned long get_stubs_size(const Elf64_Ehdr *hdr,
 			break;
 		}
 	}
-	if (i == hdr->e_shnum) {
-		pr_err("%s: doesn't contain __patchable_function_entries.\n", me->name);
-		return -ENOEXEC;
-	}
 #endif

 	pr_debug("Looks like a total of %lu stubs, max\n", relocs);
-- 
2.47.0