From 0b815825b1b0bd6762ca028e9b6631b002efb7ca Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 3 Sep 2025 20:46:45 -0700 Subject: x86/cfi: Remove __noinitretpoline and __noretpoline Commit 66f793099a63 ("x86/retpoline: Avoid retpolines for built-in __init functions") disabled retpolines in __init sections (__noinitretpoline) as a precaution against potential issues with retpolines in early boot, but it has not been a problem in practice (i.e. see Clang below). Commit 87358710c1fb ("x86/retpoline: Support retpoline builds with Clang") narrowed this to only GCC, as Clang doesn't have per-function control over retpoline emission. As such, Clang has been booting with retpolines in __init since retpoline support was introduced. Clang KCFI has been instrumenting __init since CFI was introduced. With the introduction of KCFI for GCC, KCFI instrumentation with retpolines disabled means that objtool does not construct .retpoline_sites section entries for the non-retpoline KCFI calls. At boot, the KCFI rehashing code, via __apply_fineibt(), misses all __init KCFI calls (since they are not retpolines), resulting in immediate hash mismatches: all preambles are rehashed (via .cfi_sites) and none of the __init call sites are rehashed. Remove __noinitretpoline since it provides no meaningful utility and creates problems with CFI. Additionally remove __noretpoline since it is now unused. Alternatively, cfi_rand_callers() could walk the .kcfi_traps section which is exactly the list of KCFI instrumentation sites. But it seems better to have as few differences in common instruction sequences between compilers as possible, so better to remove the special handling of retpolines in __init for GCC. Signed-off-by: Kees Cook Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20250904034656.3670313-6-kees@kernel.org --- include/linux/init.h | 8 -------- 1 file changed, 8 deletions(-) (limited to 'include/linux/init.h') diff --git a/include/linux/init.h b/include/linux/init.h index a60d32d227ee..17c1bc712e23 100644 --- a/include/linux/init.h +++ b/include/linux/init.h @@ -7,13 +7,6 @@ #include #include -/* Built-in __init functions needn't be compiled with retpoline */ -#if defined(__noretpoline) && !defined(MODULE) -#define __noinitretpoline __noretpoline -#else -#define __noinitretpoline -#endif - /* These macros are used to mark some functions or * initialized data (doesn't apply to uninitialized data) * as `initialization' functions. The kernel can take this @@ -50,7 +43,6 @@ /* These are for everybody (although not all archs will actually discard it in modules) */ #define __init __section(".init.text") __cold __latent_entropy \ - __noinitretpoline \ __no_kstack_erase #define __initdata __section(".init.data") #define __initconst __section(".init.rodata") -- cgit v1.2.3 From 6717e8f91db71641cb52855ed14c7900972ed0bc Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Wed, 17 Sep 2025 09:03:16 -0700 Subject: kbuild: Remove 'kmod_' prefix from __KBUILD_MODNAME In preparation for the objtool klp diff subcommand, remove the arbitrary 'kmod_' prefix from __KBUILD_MODNAME and instead add it explicitly in the __initcall_id() macro. This change supports the standardization of "unique" symbol naming by ensuring the non-unique portion of the name comes before the unique part. That will enable objtool to properly correlate symbols across builds. Cc: Masahiro Yamada Acked-by: Petr Mladek Tested-by: Joe Lawrence Signed-off-by: Josh Poimboeuf --- include/linux/init.h | 3 ++- scripts/Makefile.lib | 2 +- 2 files changed, 3 insertions(+), 2 deletions(-) (limited to 'include/linux/init.h') diff --git a/include/linux/init.h b/include/linux/init.h index 17c1bc712e23..40331923b9f4 100644 --- a/include/linux/init.h +++ b/include/linux/init.h @@ -200,12 +200,13 @@ extern struct module __this_module; /* Format: ____ */ #define __initcall_id(fn) \ + __PASTE(kmod_, \ __PASTE(__KBUILD_MODNAME, \ __PASTE(__, \ __PASTE(__COUNTER__, \ __PASTE(_, \ __PASTE(__LINE__, \ - __PASTE(_, fn)))))) + __PASTE(_, fn))))))) /* Format: ____ */ #define __initcall_name(prefix, __iid, id) \ diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index 1d581ba5df66..b95560266124 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -20,7 +20,7 @@ name-fix-token = $(subst $(comma),_,$(subst -,_,$1)) name-fix = $(call stringify,$(call name-fix-token,$1)) basename_flags = -DKBUILD_BASENAME=$(call name-fix,$(basetarget)) modname_flags = -DKBUILD_MODNAME=$(call name-fix,$(modname)) \ - -D__KBUILD_MODNAME=kmod_$(call name-fix-token,$(modname)) + -D__KBUILD_MODNAME=$(call name-fix-token,$(modname)) modfile_flags = -DKBUILD_MODFILE=$(call stringify,$(modfile)) _c_flags = $(filter-out $(CFLAGS_REMOVE_$(target-stem).o), \ -- cgit v1.2.3