powerpc: Do not dereference code as 'struct ppc_inst' (uprobe, code-patching, feature-fixups)

'struct ppc_inst' is an internal structure to represent an instruction,
it is not directly the representation of that instruction in text code.
It is not meant to map and dereference code.

Dereferencing code directly through 'struct ppc_inst' has two main issues:
- On powerpc, structs are expected to be 8 bytes aligned while code is
spread every 4 byte.
- Should a non prefixed instruction lie at the end of the page and the
following page not be mapped, it would generate a page fault.

In-memory code must be accessed with ppc_inst_read().
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c9a1201dd0a66b4a0f91f0fb46d9385cbf030feb.1621516826.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/uprobes.c

@@ -42,7 +42,7 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
 		return -EINVAL;
 
 	if (cpu_has_feature(CPU_FTR_ARCH_31) &&
-	    ppc_inst_prefixed(auprobe->insn) &&
+	    ppc_inst_prefixed(ppc_inst_read(&auprobe->insn)) &&
 	    (addr & 0x3f) == 60) {
 		pr_info_ratelimited("Cannot register a uprobe on 64 byte unaligned prefixed instruction\n");
 		return -EINVAL;

arch/powerpc/lib/code-patching.c

@@ -329,13 +329,13 @@ static unsigned long branch_iform_target(const struct ppc_inst *instr)
 {
 	signed long imm;
 
-	imm = ppc_inst_val(*instr) & 0x3FFFFFC;
+	imm = ppc_inst_val(ppc_inst_read(instr)) & 0x3FFFFFC;
 
 	/* If the top bit of the immediate value is set this is negative */
 	if (imm & 0x2000000)
 		imm -= 0x4000000;
 
-	if ((ppc_inst_val(*instr) & BRANCH_ABSOLUTE) == 0)
+	if ((ppc_inst_val(ppc_inst_read(instr)) & BRANCH_ABSOLUTE) == 0)
 		imm += (unsigned long)instr;
 
 	return (unsigned long)imm;
@@ -345,13 +345,13 @@ static unsigned long branch_bform_target(const struct ppc_inst *instr)
 {
 	signed long imm;
 
-	imm = ppc_inst_val(*instr) & 0xFFFC;
+	imm = ppc_inst_val(ppc_inst_read(instr)) & 0xFFFC;
 
 	/* If the top bit of the immediate value is set this is negative */
 	if (imm & 0x8000)
 		imm -= 0x10000;
 
-	if ((ppc_inst_val(*instr) & BRANCH_ABSOLUTE) == 0)
+	if ((ppc_inst_val(ppc_inst_read(instr)) & BRANCH_ABSOLUTE) == 0)
 		imm += (unsigned long)instr;
 
 	return (unsigned long)imm;

arch/powerpc/lib/feature-fixups.c

@@ -51,7 +51,7 @@ static int patch_alt_instruction(struct ppc_inst *src, struct ppc_inst *dest,
 
 	instr = ppc_inst_read(src);
 
-	if (instr_is_relative_branch(*src)) {
+	if (instr_is_relative_branch(ppc_inst_read(src))) {
 		struct ppc_inst *target = (struct ppc_inst *)branch_target(src);
 
 		/* Branch within the section doesn't need translating */