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@google.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

Author: abarnas-usys

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 skip_dry_run);
 
 #endif /* __ASSEMBLY __ */
 

arch/arm64/kernel/module.c

@@ -495,10 +495,18 @@ 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)
+			/*
+			 * Because we can reject modules that are malformed
+			 * so SCS patching fails, skip dry run and try to patch
+			 * it in place. If patching fails, the module would not
+			 * be loaded anyway.
+			 */
+			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;
+			}
 		}
 	}
 

arch/arm64/kernel/pi/map_kernel.c

@@ -104,7 +104,7 @@ 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;

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 skip_dry_run)
 {
 	int code_alignment_factor = 1;
 	bool fde_use_sdata8 = false;
@@ -277,11 +277,13 @@ int scs_patch(const u8 eh_frame[], int size)
 			}
 		} else {
 			ret = scs_handle_fde_frame(frame, code_alignment_factor,
-						   fde_use_sdata8, true);
+						   fde_use_sdata8, !skip_dry_run);
 			if (ret)
 				return ret;
-			scs_handle_fde_frame(frame, code_alignment_factor,
-					     fde_use_sdata8, false);
+
+			if (!skip_dry_run)
+				scs_handle_fde_frame(frame, code_alignment_factor,
+						     fde_use_sdata8, false);
 		}
 
 		p += sizeof(frame->size) + frame->size;

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 skip_dry_run);
 
 void map_range(phys_addr_t *pte, u64 start, u64 end, phys_addr_t pa,
 	       pgprot_t prot, int level, pte_t *tbl, bool may_use_cont,