[v4,18/27] xen: Adapt assembly for PIE support
diff mbox

Message ID 20180529221625.33541-19-thgarnie@google.com
State New
Headers show

Commit Message

Thomas Garnier May 29, 2018, 10:15 p.m. UTC
Change the assembly code to use the new _ASM_MOVABS macro which get a
symbol reference while being PIE compatible. Adapt the relocation tool
to ignore 32-bit Xen code.

Position Independent Executable (PIE) support will allow to extend the
KASLR randomization range 0xffffffff80000000.

Signed-off-by: Thomas Garnier <thgarnie@google.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/tools/relocs.c | 16 +++++++++++++++-
 arch/x86/xen/xen-head.S | 11 ++++++-----
 arch/x86/xen/xen-pvh.S  | 13 +++++++++----
 3 files changed, 30 insertions(+), 10 deletions(-)

Comments

Boris Ostrovsky June 1, 2018, 3:44 p.m. UTC | #1
On 05/29/2018 06:15 PM, Thomas Garnier wrote:
> diff --git a/arch/x86/xen/xen-pvh.S b/arch/x86/xen/xen-pvh.S
> index ca2d3b2bf2af..82ba89ba8bb3 100644
> --- a/arch/x86/xen/xen-pvh.S
> +++ b/arch/x86/xen/xen-pvh.S
> @@ -114,8 +114,8 @@ ENTRY(pvh_start_xen)
>  	call xen_prepare_pvh
>  
>  	/* startup_64 expects boot_params in %rsi. */
> -	mov $_pa(pvh_bootparams), %rsi
> -	mov $_pa(startup_64), %rax
> +	movabs $_pa(pvh_bootparams), %rsi
> +	movabs $_pa(startup_64), %rax
>  	jmp *%rax
>  
>  #else /* CONFIG_X86_64 */
> @@ -161,10 +161,15 @@ END(pvh_start_xen)
>  
>  	.section ".init.data","aw"
>  	.balign 8
> +	/*
> +	 * Use a quad for _pa(gdt_start) because PIE does not understand a
> +	 * long is enough. The resulting value will still be in the lower long
> +	 * part.
> +	 */
>  gdt:
>  	.word gdt_end - gdt_start
> -	.long _pa(gdt_start)
> -	.word 0
> +	.quad _pa(gdt_start)


With this becoming .quad 32-bit compilation fails:

/data/root/linux/arch/x86/xen/xen-pvh.S: Assembler messages:
/data/root/linux/arch/x86/xen/xen-pvh.S:147: Error: cannot represent
relocation type BFD_RELOC_64


-boris


> +	.balign 8
>  gdt_start:
>  	.quad 0x0000000000000000            /* NULL descriptor */
>  #ifdef CONFIG_X86_64
Thomas Garnier June 1, 2018, 3:53 p.m. UTC | #2
On Fri, Jun 1, 2018 at 8:40 AM Boris Ostrovsky
<boris.ostrovsky@oracle.com> wrote:
>
> On 05/29/2018 06:15 PM, Thomas Garnier wrote:
> > diff --git a/arch/x86/xen/xen-pvh.S b/arch/x86/xen/xen-pvh.S
> > index ca2d3b2bf2af..82ba89ba8bb3 100644
> > --- a/arch/x86/xen/xen-pvh.S
> > +++ b/arch/x86/xen/xen-pvh.S
> > @@ -114,8 +114,8 @@ ENTRY(pvh_start_xen)
> >       call xen_prepare_pvh
> >
> >       /* startup_64 expects boot_params in %rsi. */
> > -     mov $_pa(pvh_bootparams), %rsi
> > -     mov $_pa(startup_64), %rax
> > +     movabs $_pa(pvh_bootparams), %rsi
> > +     movabs $_pa(startup_64), %rax
> >       jmp *%rax
> >
> >  #else /* CONFIG_X86_64 */
> > @@ -161,10 +161,15 @@ END(pvh_start_xen)
> >
> >       .section ".init.data","aw"
> >       .balign 8
> > +     /*
> > +      * Use a quad for _pa(gdt_start) because PIE does not understand a
> > +      * long is enough. The resulting value will still be in the lower long
> > +      * part.
> > +      */
> >  gdt:
> >       .word gdt_end - gdt_start
> > -     .long _pa(gdt_start)
> > -     .word 0
> > +     .quad _pa(gdt_start)
>
>
> With this becoming .quad 32-bit compilation fails:
>
> /data/root/linux/arch/x86/xen/xen-pvh.S: Assembler messages:
> /data/root/linux/arch/x86/xen/xen-pvh.S:147: Error: cannot represent
> relocation type BFD_RELOC_64

Thanks, I will look to fix this in the next patch set and run a full
32-bit build.

>
>
> -boris
>
>
> > +     .balign 8
> >  gdt_start:
> >       .quad 0x0000000000000000            /* NULL descriptor */
> >  #ifdef CONFIG_X86_64
>

Patch
diff mbox

diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index a35cc337f883..29283ad3950f 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -832,6 +832,16 @@  static int is_percpu_sym(ElfW(Sym) *sym, const char *symname)
 		strncmp(symname, "init_per_cpu_", 13);
 }
 
+/*
+ * Check if the 32-bit relocation is within the xenpvh 32-bit code.
+ * If so, ignores it.
+ */
+static int is_in_xenpvh_assembly(ElfW(Addr) offset)
+{
+	ElfW(Sym) *sym = sym_lookup("pvh_start_xen");
+	return sym && (offset >= sym->st_value) &&
+		(offset < (sym->st_value + sym->st_size));
+}
 
 static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
 		      const char *symname)
@@ -895,8 +905,12 @@  static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
 		 * the relocations are processed.
 		 * Make sure that the offset will fit.
 		 */
-		if (r_type != R_X86_64_64 && (int32_t)offset != (int64_t)offset)
+		if (r_type != R_X86_64_64 &&
+		    (int32_t)offset != (int64_t)offset) {
+			if (is_in_xenpvh_assembly(offset))
+				break;
 			die("Relocation offset doesn't fit in 32 bits\n");
+		}
 
 		if (r_type == R_X86_64_64)
 			add_reloc(&relocs64, offset);
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 5077ead5e59c..4418ff0a1d96 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -28,14 +28,15 @@  ENTRY(startup_xen)
 
 	/* Clear .bss */
 	xor %eax,%eax
-	mov $__bss_start, %_ASM_DI
-	mov $__bss_stop, %_ASM_CX
+	_ASM_MOVABS $__bss_start, %_ASM_DI
+	_ASM_MOVABS $__bss_stop, %_ASM_CX
 	sub %_ASM_DI, %_ASM_CX
 	shr $__ASM_SEL(2, 3), %_ASM_CX
 	rep __ASM_SIZE(stos)
 
-	mov %_ASM_SI, xen_start_info
-	mov $init_thread_union+THREAD_SIZE, %_ASM_SP
+	_ASM_MOVABS $xen_start_info, %_ASM_AX
+	_ASM_MOV %_ASM_SI, (%_ASM_AX)
+	_ASM_MOVABS $init_thread_union+THREAD_SIZE, %_ASM_SP
 
 #ifdef CONFIG_X86_64
 	/* Set up %gs.
@@ -46,7 +47,7 @@  ENTRY(startup_xen)
 	 * init data section till per cpu areas are set up.
 	 */
 	movl	$MSR_GS_BASE,%ecx
-	movq	$INIT_PER_CPU_VAR(irq_stack_union),%rax
+	movabsq	$INIT_PER_CPU_VAR(irq_stack_union),%rax
 	cdq
 	wrmsr
 #endif
diff --git a/arch/x86/xen/xen-pvh.S b/arch/x86/xen/xen-pvh.S
index ca2d3b2bf2af..82ba89ba8bb3 100644
--- a/arch/x86/xen/xen-pvh.S
+++ b/arch/x86/xen/xen-pvh.S
@@ -114,8 +114,8 @@  ENTRY(pvh_start_xen)
 	call xen_prepare_pvh
 
 	/* startup_64 expects boot_params in %rsi. */
-	mov $_pa(pvh_bootparams), %rsi
-	mov $_pa(startup_64), %rax
+	movabs $_pa(pvh_bootparams), %rsi
+	movabs $_pa(startup_64), %rax
 	jmp *%rax
 
 #else /* CONFIG_X86_64 */
@@ -161,10 +161,15 @@  END(pvh_start_xen)
 
 	.section ".init.data","aw"
 	.balign 8
+	/*
+	 * Use a quad for _pa(gdt_start) because PIE does not understand a
+	 * long is enough. The resulting value will still be in the lower long
+	 * part.
+	 */
 gdt:
 	.word gdt_end - gdt_start
-	.long _pa(gdt_start)
-	.word 0
+	.quad _pa(gdt_start)
+	.balign 8
 gdt_start:
 	.quad 0x0000000000000000            /* NULL descriptor */
 #ifdef CONFIG_X86_64