Re: [PATCH] powerpc/module_64: Fix livepatching for RO modules

[Michael Ellerman <mpe@ellerman.id.au>]

Russell Currey <ruscur@russell.cc> writes:
> On Tue, 2021-12-07 at 09:44 -0500, Joe Lawrence wrote:
>> On 11/23/21 3:15 AM, Russell Currey wrote:
>> 
>> [[ cc += livepatching list ]]
>> 
>> Hi Russell,
>> 
>> Thanks for writing a minimal fix for stable / backporting.  As I
>> mentioned on the github issue [1], this avoided the crashes I
>> reported
>> here and over on kpatch github [2].  I wasn't sure if this is the
>> final
>> version for stable, but feel free to add my:
>> 
>> Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
>
> Thanks Joe, as per the discussions on GitHub I think we're fine to use
> this patch for a fix for stable (unless there's new issues found or
> additional community feedback etc).

Hmm, I read the GitHub discussion as being that you were going to do
another version, which is why I haven't picked this up. But I guess you
and Christophe were talking about the non-minimal fix.

I know we want this to be minimal, but I think it should be checking
that patch_instruction() isn't failing.

Incremental diff to do that is below. It boots OK, are you able to throw
a livepatch test at it?

cheers



diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index c25ef36c3ef4..5d77d3f5fbb5 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -429,8 +429,9 @@ static inline int create_stub(const Elf64_Shdr *sechdrs,
 		return create_ftrace_stub(entry, addr, me);
 
 	for (i = 0; i < sizeof(ppc64_stub_insns) / sizeof(u32); i++) {
-		patch_instruction(&entry->jump[i],
-				  ppc_inst(ppc64_stub_insns[i]));
+		if (patch_instruction(&entry->jump[i],
+				      ppc_inst(ppc64_stub_insns[i])))
+			return 0;
 	}
 
 	/* Stub uses address relative to r2. */
@@ -442,19 +443,24 @@ static inline int create_stub(const Elf64_Shdr *sechdrs,
 	}
 	pr_debug("Stub %p get data from reladdr %li\n", entry, reladdr);
 
-	patch_instruction(&entry->jump[0],
-			  ppc_inst(entry->jump[0] | PPC_HA(reladdr)));
-	patch_instruction(&entry->jump[1],
-			  ppc_inst(entry->jump[1] | PPC_LO(reladdr)));
+	if (patch_instruction(&entry->jump[0],
+			      ppc_inst(entry->jump[0] | PPC_HA(reladdr))))
+		return 0;
+
+	if (patch_instruction(&entry->jump[1],
+			  ppc_inst(entry->jump[1] | PPC_LO(reladdr))))
+		return 0;
 
 	// func_desc_t is 8 bytes if ABIv2, else 16 bytes
 	desc = func_desc(addr);
 	for (i = 0; i < sizeof(func_desc_t) / sizeof(u32); i++) {
-		patch_instruction(((u32 *)&entry->funcdata) + i,
-				  ppc_inst(((u32 *)(&desc))[i]));
+		if (patch_instruction(((u32 *)&entry->funcdata) + i,
+				      ppc_inst(((u32 *)(&desc))[i])))
+			return 0;
 	}
 
-	patch_instruction(&entry->magic, ppc_inst(STUB_MAGIC));
+	if (patch_instruction(&entry->magic, ppc_inst(STUB_MAGIC)))
+		return 0;
 
 	return 1;
 }
@@ -509,8 +515,11 @@ static int restore_r2(const char *name, u32 *instruction, struct module *me)
 			me->name, *instruction, instruction);
 		return 0;
 	}
+
 	/* ld r2,R2_STACK_OFFSET(r1) */
-	patch_instruction(instruction, ppc_inst(PPC_INST_LD_TOC));
+	if (patch_instruction(instruction, ppc_inst(PPC_INST_LD_TOC)))
+		return 0;
+
 	return 1;
 }
 
@@ -652,7 +661,10 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 			/* Only replace bits 2 through 26 */
 			value = (*(uint32_t *)location & ~0x03fffffc)
 				| (value & 0x03fffffc);
-			patch_instruction((u32 *)location, ppc_inst(value));
+
+			if (patch_instruction((u32 *)location, ppc_inst(value)))
+				return -EFAULT;
+
 			break;
 
 		case R_PPC64_REL64: