[PATCH v2] x86/alternative: Consistently patch SMP locks in vmlinux and modules

[Julian Pidancet]

The alternatives_smp_module_add() function restricts patching of SMP
lock prefixes to the text address range passed as an argument.

For vmlinux, patching all the instructions located between the _text and
_etext symbols is allowed. That includes the .text section but also
other sections such as .text.hot and .text.unlikely.

As per the comment inside the 'struct smp_alt_module' definition, the
original purpose of this restriction is to avoid patching the init code.

For modules, the current code only allows patching instructions located
inside the .text segment, excluding other sections such as .text.hot or
.text.unlikely, which may need patching.

Make patching of the kernel core and modules more consistent, by
allowing all text sections of modules except .init.text to be patched in
module_finalize().

For that, use mod->core_layout.base/mod->core_layout.text_size as the
address range allowed to be patched, which include all the code sections
except the init code.

Signed-off-by: Julian Pidancet <julian.pidancet@xxxxxxxxxx>
---
Public tests: https://gist.github.com/jpidancet/1ee457623426f3e3902a28edaf2c80d0
Related thread: https://marc.info/?t=130864398400006

V1 -> V2: Reworded the commit description.

 arch/x86/kernel/module.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index c032edcd3d95..b1e6e45a5e10 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -251,14 +251,12 @@ int module_finalize(const Elf_Ehdr *hdr,
 		    const Elf_Shdr *sechdrs,
 		    struct module *me)
 {
-	const Elf_Shdr *s, *text = NULL, *alt = NULL, *locks = NULL,
-		*para = NULL, *orc = NULL, *orc_ip = NULL,
-		*retpolines = NULL, *returns = NULL, *ibt_endbr = NULL;
+	const Elf_Shdr *s, *alt = NULL, *locks = NULL, *para = NULL,
+		*orc = NULL, *orc_ip = NULL, *retpolines = NULL,
+		*returns = NULL, *ibt_endbr = NULL;
 	char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
 
 	for (s = sechdrs; s < sechdrs + hdr->e_shnum; s++) {
-		if (!strcmp(".text", secstrings + s->sh_name))
-			text = s;
 		if (!strcmp(".altinstructions", secstrings + s->sh_name))
 			alt = s;
 		if (!strcmp(".smp_locks", secstrings + s->sh_name))
@@ -302,12 +300,13 @@ int module_finalize(const Elf_Ehdr *hdr,
 		void *iseg = (void *)ibt_endbr->sh_addr;
 		apply_ibt_endbr(iseg, iseg + ibt_endbr->sh_size);
 	}
-	if (locks && text) {
+	if (locks) {
 		void *lseg = (void *)locks->sh_addr;
-		void *tseg = (void *)text->sh_addr;
+		void *text = me->core_layout.base;
+		void *text_end = text + me->core_layout.text_size;
 		alternatives_smp_module_add(me, me->name,
 					    lseg, lseg + locks->sh_size,
-					    tseg, tseg + text->sh_size);
+					    text, text_end);
 	}
 
 	if (orc && orc_ip)
-- 
2.37.3