linux-kernel - [PATCH 1/2] arch: arm64: Fail module loading if dynamic SCS patching fails

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Message-ID: <20250919122321.946462-2-abarnas@google.com>
Date: Fri, 19 Sep 2025 12:23:20 +0000
From: "Adrian Barnaś" <abarnas@...gle.com>
To: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc: "Adrian Barnaś" <abarnas@...gle.com>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Ard Biesheuvel <ardb@...nel.org>, Dylan Hatch <dylanbhatch@...gle.com>, 
	Mark Rutland <mark.rutland@....com>
Subject: [PATCH 1/2] arch: arm64: Fail module loading if dynamic SCS patching fails

Disallow a module to load if SCS dynamic patching fails for its code. For
module loading, instead of running a dry-run to check for patching errors,
try to run patching in the first run and propagate any errors so module
loading will fail.

Signed-off-by: Adrian Barnaś <abarnas@...gle.com>
---
 arch/arm64/include/asm/scs.h      |  2 +-
 arch/arm64/kernel/module.c        |  6 ++++--
 arch/arm64/kernel/pi/map_kernel.c |  2 +-
 arch/arm64/kernel/pi/patch-scs.c  | 15 +++++++++++----
 arch/arm64/kernel/pi/pi.h         |  2 +-
 5 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/scs.h b/arch/arm64/include/asm/scs.h
index a76f9b387a26..ffcfcda87f10 100644
--- a/arch/arm64/include/asm/scs.h
+++ b/arch/arm64/include/asm/scs.h
@@ -53,7 +53,7 @@ enum {
 	EDYNSCS_INVALID_CFA_OPCODE		= 4,
 };
 
-int __pi_scs_patch(const u8 eh_frame[], int size);
+int __pi_scs_patch(const u8 eh_frame[], int size, bool is_module);
 
 #endif /* __ASSEMBLY __ */
 
diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index 40148d2725ce..5d6d228c6156 100644
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -484,10 +484,12 @@ int module_finalize(const Elf_Ehdr *hdr,
 	if (scs_is_dynamic()) {
 		s = find_section(hdr, sechdrs, ".init.eh_frame");
 		if (s) {
-			ret = __pi_scs_patch((void *)s->sh_addr, s->sh_size);
-			if (ret)
+			ret = __pi_scs_patch((void *)s->sh_addr, s->sh_size, true);
+			if (ret) {
 				pr_err("module %s: error occurred during dynamic SCS patching (%d)\n",
 				       me->name, ret);
+				return -ENOEXEC;
+			}
 		}
 	}
 
diff --git a/arch/arm64/kernel/pi/map_kernel.c b/arch/arm64/kernel/pi/map_kernel.c
index 0f4bd7771859..7187eda9e8a5 100644
--- a/arch/arm64/kernel/pi/map_kernel.c
+++ b/arch/arm64/kernel/pi/map_kernel.c
@@ -98,7 +98,7 @@ static void __init map_kernel(u64 kaslr_offset, u64 va_offset, int root_level)
 
 		if (enable_scs) {
 			scs_patch(__eh_frame_start + va_offset,
-				  __eh_frame_end - __eh_frame_start);
+				  __eh_frame_end - __eh_frame_start, false);
 			asm("ic ialluis");
 
 			dynamic_scs_is_enabled = true;
diff --git a/arch/arm64/kernel/pi/patch-scs.c b/arch/arm64/kernel/pi/patch-scs.c
index 55d0cd64ef71..78266fb1fa61 100644
--- a/arch/arm64/kernel/pi/patch-scs.c
+++ b/arch/arm64/kernel/pi/patch-scs.c
@@ -225,7 +225,7 @@ static int scs_handle_fde_frame(const struct eh_frame *frame,
 	return 0;
 }
 
-int scs_patch(const u8 eh_frame[], int size)
+int scs_patch(const u8 eh_frame[], int size, bool is_module)
 {
 	int code_alignment_factor = 1;
 	bool fde_use_sdata8 = false;
@@ -276,12 +276,19 @@ int scs_patch(const u8 eh_frame[], int size)
 				return EDYNSCS_INVALID_CIE_SDATA_SIZE;
 			}
 		} else {
+			/*
+			 * For loadable module instead of running a dry run try
+			 * to patch scs instruction in place and trigger error
+			 * if failed, to prevent module loading.
+			 */
 			ret = scs_handle_fde_frame(frame, code_alignment_factor,
-						   fde_use_sdata8, true);
+						   fde_use_sdata8, !is_module);
 			if (ret)
 				return ret;
-			scs_handle_fde_frame(frame, code_alignment_factor,
-					     fde_use_sdata8, false);
+
+			if (!is_module)
+				scs_handle_fde_frame(frame, code_alignment_factor,
+						     fde_use_sdata8, false);
 		}
 
 		p += sizeof(frame->size) + frame->size;
diff --git a/arch/arm64/kernel/pi/pi.h b/arch/arm64/kernel/pi/pi.h
index 46cafee7829f..4ccbba24fadc 100644
--- a/arch/arm64/kernel/pi/pi.h
+++ b/arch/arm64/kernel/pi/pi.h
@@ -27,7 +27,7 @@ extern pgd_t init_pg_dir[], init_pg_end[];
 void init_feature_override(u64 boot_status, const void *fdt, int chosen);
 u64 kaslr_early_init(void *fdt, int chosen);
 void relocate_kernel(u64 offset);
-int scs_patch(const u8 eh_frame[], int size);
+int scs_patch(const u8 eh_frame[], int size, bool is_module);
 
 void map_range(u64 *pgd, u64 start, u64 end, u64 pa, pgprot_t prot,
 	       int level, pte_t *tbl, bool may_use_cont, u64 va_offset);
-- 
2.51.0.534.gc79095c0ca-goog