linux-kernel - Re: [PATCH v2 15/25] objtool: Rework ibt and extricate from stack validation

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Date:   Fri, 22 Apr 2022 12:50:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 15/25] objtool: Rework ibt and extricate from stack
 validation

On Wed, Apr 20, 2022 at 07:25:16PM +0200, Miroslav Benes wrote:
> A nit and it was there even before this patch...
> 
> > -static struct instruction *
> > -validate_ibt_reloc(struct objtool_file *file, struct reloc *reloc)
> > -{
> > -	struct instruction *dest;
> > -	struct section *sec;
> > -	unsigned long off;
> > -
> > -	sec = reloc->sym->sec;
> > -	off = reloc->sym->offset;
> > -
> > -	if ((reloc->sec->base->sh.sh_flags & SHF_EXECINSTR) &&
> > -	    (reloc->type == R_X86_64_PC32 || reloc->type == R_X86_64_PLT32))
> > -		off += arch_dest_reloc_offset(reloc->addend);
> 
> here...
> 
> > +static int validate_ibt_insn(struct objtool_file *file, struct instruction *insn)
> > +{
> 
> ...
> > +		off = reloc->sym->offset;
> > +		if (reloc->type == R_X86_64_PC32 || reloc->type == R_X86_64_PLT32)
> > +			off += arch_dest_reloc_offset(reloc->addend);
> > +		else
> > +			off += reloc->addend;
> 
> it looks kind of strange to have arch_dest_reloc_offset() and still 
> reference arch-specific relocation types here. On the other hand it seems 
> difficult to achieve complete arch-agnostic code, so take it just as a 
> note and maybe someone porting objtool to a different architecture will 
> split the code, make it all arch-independent and all will be nice and 
> shiny.

Something like so perhaps? Seems to build and boot x86_64-defconfig.

---
 tools/objtool/arch/x86/decode.c      |  9 +++++++--
 tools/objtool/check.c                | 18 +++++++-----------
 tools/objtool/include/objtool/arch.h |  2 +-
 3 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 8b990a52aada..775e1963ecfc 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -63,9 +63,14 @@ bool arch_callee_saved_reg(unsigned char reg)
 	}
 }
 
-unsigned long arch_dest_reloc_offset(int addend)
+unsigned long arch_dest_reloc_offset(struct reloc *reloc)
 {
-	return addend + 4;
+	unsigned long offset = reloc->sym->offset + reloc->addend;
+
+	if (reloc->type == R_X86_64_PC32 || reloc->type == R_X86_64_PLT32)
+		offset += 4;
+
+	return offset;
 }
 
 unsigned long arch_jump_destination(struct instruction *insn)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 2063f9fea1a2..5752013dd6e8 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1295,7 +1295,7 @@ static int add_jump_destinations(struct objtool_file *file)
 			dest_off = arch_jump_destination(insn);
 		} else if (reloc->sym->type == STT_SECTION) {
 			dest_sec = reloc->sym->sec;
-			dest_off = arch_dest_reloc_offset(reloc->addend);
+			dest_off = arch_dest_reloc_offset(reloc);
 		} else if (reloc->sym->retpoline_thunk) {
 			add_retpoline_call(file, insn);
 			continue;
@@ -1308,8 +1308,7 @@ static int add_jump_destinations(struct objtool_file *file)
 			continue;
 		} else if (reloc->sym->sec->idx) {
 			dest_sec = reloc->sym->sec;
-			dest_off = reloc->sym->sym.st_value +
-				   arch_dest_reloc_offset(reloc->addend);
+			dest_off = arch_dest_reloc_offset(reloc);
 		} else {
 			/* non-func asm code jumping to another file */
 			continue;
@@ -1413,7 +1412,7 @@ static int add_call_destinations(struct objtool_file *file)
 			}
 
 		} else if (reloc->sym->type == STT_SECTION) {
-			dest_off = arch_dest_reloc_offset(reloc->addend);
+			dest_off = arch_dest_reloc_offset(reloc);
 			dest = find_call_destination(reloc->sym->sec, dest_off);
 			if (!dest) {
 				WARN_FUNC("can't find call dest symbol at %s+0x%lx",
@@ -3031,6 +3030,7 @@ static inline const char *call_dest_name(struct instruction *insn)
 static bool pv_call_dest(struct objtool_file *file, struct instruction *insn)
 {
 	struct symbol *target;
+	unsigned long offset;
 	struct reloc *rel;
 	int idx;
 
@@ -3038,7 +3038,8 @@ static bool pv_call_dest(struct objtool_file *file, struct instruction *insn)
 	if (!rel || strcmp(rel->sym->name, "pv_ops"))
 		return false;
 
-	idx = (arch_dest_reloc_offset(rel->addend) / sizeof(void *));
+	offset = arch_dest_reloc_offset(rel) - rel->sym->offset;
+	idx = offset / sizeof(void *);
 
 	if (file->pv_ops[idx].clean)
 		return true;
@@ -3709,12 +3710,7 @@ static int validate_ibt_insn(struct objtool_file *file, struct instruction *insn
 		if (reloc->sym->static_call_tramp)
 			continue;
 
-		off = reloc->sym->offset;
-		if (reloc->type == R_X86_64_PC32 || reloc->type == R_X86_64_PLT32)
-			off += arch_dest_reloc_offset(reloc->addend);
-		else
-			off += reloc->addend;
-
+		off = arch_dest_reloc_offset(reloc);
 		dest = find_insn(file, reloc->sym->sec, off);
 		if (!dest)
 			continue;
diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 9b19cc304195..57562eaa0967 100644
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -81,7 +81,7 @@ bool arch_callee_saved_reg(unsigned char reg);
 
 unsigned long arch_jump_destination(struct instruction *insn);
 
-unsigned long arch_dest_reloc_offset(int addend);
+unsigned long arch_dest_reloc_offset(struct reloc *reloc);
 
 const char *arch_nop_insn(int len);
 const char *arch_ret_insn(int len);