Patch "x86/module: Detect and skip invalid relocations" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

x86/module: Detect and skip invalid relocations

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-module-detect-and-skip-invalid-relocations.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Josh Poimboeuf <[email protected]>
Date: Fri, 3 Nov 2017 07:58:54 -0500
Subject: x86/module: Detect and skip invalid relocations

From: Josh Poimboeuf <[email protected]>

commit eda9cec4c9a12208a6f69fbe68f72a6311d50032 upstream.

There have been some cases where external tooling (e.g., kpatch-build) creates a corrupt relocation which targets the wrong address. This is a silent failure which can corrupt memory in unexpected places.

On x86, the bytes of data being overwritten by relocations are always initialized to zero beforehand. Use that knowledge to add sanity checks to detect such cases before they corrupt memory.

---
 arch/x86/kernel/module.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

@@ -171,19 +171,27 @@ int apply_relocate_add(Elf64_Shdr *sechd
 		case R_X86_64_NONE:
 			break;
 		case R_X86_64_64:
+			if (*(u64 *)loc != 0)
+				goto invalid_relocation;
 			*(u64 *)loc = val;
 			break;
 		case R_X86_64_32:
+			if (*(u32 *)loc != 0)
+				goto invalid_relocation;
 			*(u32 *)loc = val;
 			if (val != *(u32 *)loc)
 				goto overflow;
 			break;
 		case R_X86_64_32S:
+			if (*(s32 *)loc != 0)
+				goto invalid_relocation;
 			*(s32 *)loc = val;
 			if ((s64)val != *(s32 *)loc)
 				goto overflow;
 			break;
 		case R_X86_64_PC32:
+			if (*(u32 *)loc != 0)
+				goto invalid_relocation;
 			val -= (u64)loc;
 			*(u32 *)loc = val;
 #if 0

@@ -199,6 +207,11 @@ int apply_relocate_add(Elf64_Shdr *sechd
 	}
 	return 0;
 
+invalid_relocation:
+	pr_err("x86/modules: Skipping invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
+	       (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
+	return -ENOEXEC;
+
 overflow:
 	pr_err("overflow in relocation type %d val %Lx\n",
 	       (int)ELF64_R_TYPE(rel[i].r_info), val);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/x86-boot-objtool-annotate-indirect-jump-in-secondary_startup_64.patch queue-4.9/x86-module-detect-and-skip-invalid-relocations.patch queue-4.9/nospec-include-asm-barrier.h-dependency.patch queue-4.9/x86-speculation-objtool-annotate-indirect-calls-jumps-for-objtool.patch queue-4.9/x86-paravirt-objtool-annotate-indirect-calls.patch queue-4.9/nospec-kill-array_index_nospec_mask_check.patch