Linux Virtualization - Jul 2019 - [PATCH v9 10/11] x86/paravirt: Adapt assembly for PIE support

Minor changes based on feedback and rebase from v8.

Splitting the previous serie in two. This part contains assembly code
changes required for PIE but without any direct dependencies with the
rest of the patchset.

Changes:
 - patch v9 (assembly):
   - Moved to relative reference for sync_core based on feedback.
   - x86/crypto had multiple algorithms deleted, removed PIE changes to them.
   - fix typo on comment end line.
 - patch v8 (assembly):
   - Fix issues in crypto changes (thanks to Eric Biggers).
   - Remove unnecessary jump table change.
   - Change author and signoff to chromium email address.
 - patch v7 (assembly):
   - Split patchset and reorder changes.
 - patch v6:
   - Rebase on latest changes in jump tables and crypto.
   - Fix wording on couple commits.
   - Revisit checkpatch warnings.
   - Moving to @chromium.org.
 - patch v5:
   - Adapt new crypto modules for PIE.
   - Improve per-cpu commit message.
   - Fix xen 32-bit build error with .quad.
   - Remove extra code for ftrace.
 - patch v4:
   - Simplify early boot by removing global variables.
   - Modify the mcount location script for __mcount_loc intead of the address
     read in the ftrace implementation.
   - Edit commit description to explain better where the kernel can be located.
   - Streamlined the testing done on each patch proposal. Always testing
     hibernation, suspend, ftrace and kprobe to ensure no regressions.
 - patch v3:
   - Update on message to describe longer term PIE goal.
   - Minor change on ftrace if condition.
   - Changed code using xchgq.
 - patch v2:
   - Adapt patch to work post KPTI and compiler changes
   - Redo all performance testing with latest configs and compilers
   - Simplify mov macro on PIE (MOVABS now)
   - Reduce GOT footprint
 - patch v1:
   - Simplify ftrace implementation.
   - Use gcc mstack-protector-guard-reg=%gs with PIE when possible.
 - rfc v3:
   - Use --emit-relocs instead of -pie to reduce dynamic relocation space on
     mapped memory. It also simplifies the relocation process.
   - Move the start the module section next to the kernel. Remove the need for
     -mcmodel=large on modules. Extends module space from 1 to 2G maximum.
   - Support for XEN PVH as 32-bit relocations can be ignored with
     --emit-relocs.
   - Support for GOT relocations previously done automatically with -pie.
   - Remove need for dynamic PLT in modules.
   - Support dymamic GOT for modules.
 - rfc v2:
   - Add support for global stack cookie while compiler default to fs without
     mcmodel=kernel
   - Change patch 7 to correctly jump out of the identity mapping on kexec load
     preserve.

These patches make some of the changes necessary to build the kernel as
Position Independent Executable (PIE) on x86_64. Another patchset will
add the PIE option and larger architecture changes.

The patches:
 - 1, 3-11: Change in assembly code to be PIE compliant.
 - 2: Add a new _ASM_MOVABS macro to fetch a symbol address generically.

diffstat:
 crypto/aegis128-aesni-asm.S         |    6 +-
 crypto/aesni-intel_asm.S            |    8 +--
 crypto/aesni-intel_avx-x86_64.S     |    3 -
 crypto/camellia-aesni-avx-asm_64.S  |   42 +++++++--------
 crypto/camellia-aesni-avx2-asm_64.S |   44 ++++++++--------
 crypto/camellia-x86_64-asm_64.S     |    8 +--
 crypto/cast5-avx-x86_64-asm_64.S    |   50 ++++++++++--------
 crypto/cast6-avx-x86_64-asm_64.S    |   44 +++++++++-------
 crypto/des3_ede-asm_64.S            |   96 ++++++++++++++++++++++++------------
 crypto/ghash-clmulni-intel_asm.S    |    4 -
 crypto/glue_helper-asm-avx.S        |    4 -
 crypto/glue_helper-asm-avx2.S       |    6 +-
 crypto/sha256-avx2-asm.S            |   18 ++++--
 entry/entry_64.S                    |   16 ++++--
 include/asm/alternative.h           |    6 +-
 include/asm/asm.h                   |    1 
 include/asm/paravirt_types.h        |   25 +++++++--
 include/asm/pm-trace.h              |    2 
 include/asm/processor.h             |    6 +-
 kernel/acpi/wakeup_64.S             |   31 ++++++-----
 kernel/head_64.S                    |   16 +++---
 kernel/relocate_kernel_64.S         |    2 
 power/hibernate_asm_64.S            |    4 -
 23 files changed, 261 insertions(+), 181 deletions(-)

Patchset is based on next-20190729.

if PIE is enabled, switch the paravirt assembly constraints to be
compatible. The %c/i constrains generate smaller code so is kept by
default.

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

Signed-off-by: Thomas Garnier <thgarnie at chromium.org>
Acked-by: Juergen Gross <jgross at suse.com>
---
 arch/x86/include/asm/paravirt_types.h | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index 70b654f3ffe5..fd7dc37d0010 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -338,9 +338,25 @@ extern struct paravirt_patch_template pv_ops;
 #define PARAVIRT_PATCH(x)					\
 	(offsetof(struct paravirt_patch_template, x) / sizeof(void *))
 
+#ifdef CONFIG_X86_PIE
+#define paravirt_opptr_call "a"
+#define paravirt_opptr_type "p"
+
+/*
+ * Alternative patching requires a maximum of 7 bytes but the relative call is
+ * only 6 bytes. If PIE is enabled, add an additional nop to the call
+ * instruction to ensure patching is possible.
+ */
+#define PARAVIRT_CALL_POST  "nop;"
+#else
+#define paravirt_opptr_call "c"
+#define paravirt_opptr_type "i"
+#define PARAVIRT_CALL_POST  ""
+#endif
+
 #define paravirt_type(op)				\
 	[paravirt_typenum] "i" (PARAVIRT_PATCH(op)),	\
-	[paravirt_opptr] "i" (&(pv_ops.op))
+	[paravirt_opptr] paravirt_opptr_type (&(pv_ops.op))
 #define paravirt_clobber(clobber)		\
 	[paravirt_clobber] "i" (clobber)
 
@@ -379,9 +395,10 @@ int paravirt_disable_iospace(void);
  * offset into the paravirt_patch_template structure, and can therefore be
  * freely converted back into a structure offset.
  */
-#define PARAVIRT_CALL					\
-	ANNOTATE_RETPOLINE_SAFE				\
-	"call *%c[paravirt_opptr];"
+#define PARAVIRT_CALL						\
+	ANNOTATE_RETPOLINE_SAFE					\
+	"call *%" paravirt_opptr_call "[paravirt_opptr];"	\
+	PARAVIRT_CALL_POST
 
 /*
  * These macros are intended to wrap calls through one of the paravirt
-- 
2.22.0.770.g0f2c4a37fd-goog

On Tue, Jul 30, 2019 at 12:12:54PM -0700, Thomas Garnier
wrote:
> if PIE is enabled, switch the paravirt assembly constraints to be
> compatible. The %c/i constrains generate smaller code so is kept by
> default.
> 
> Position Independent Executable (PIE) support will allow to extend the
> KASLR randomization range below 0xffffffff80000000.
> 
> Signed-off-by: Thomas Garnier <thgarnie at chromium.org>
> Acked-by: Juergen Gross <jgross at suse.com>
> ---
>  arch/x86/include/asm/paravirt_types.h | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
> index 70b654f3ffe5..fd7dc37d0010 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -338,9 +338,25 @@ extern struct paravirt_patch_template pv_ops;
>  #define PARAVIRT_PATCH(x)					\
>  	(offsetof(struct paravirt_patch_template, x) / sizeof(void *))
>  
> +#ifdef CONFIG_X86_PIE
> +#define paravirt_opptr_call "a"
> +#define paravirt_opptr_type "p"
> +
> +/*
> + * Alternative patching requires a maximum of 7 bytes but the relative
call is
> + * only 6 bytes. If PIE is enabled, add an additional nop to the call
> + * instruction to ensure patching is possible.
> + */
> +#define PARAVIRT_CALL_POST  "nop;"
I'm confused; where does the 7 come from? The relative call is 6 bytes,
a normal call is 5 bytes (which is what we normally replace them with),
and the longest 'native' sequence we seem to have is also 6 bytes
(.cpu_usergs_sysret64).
> +#else
> +#define paravirt_opptr_call "c"
> +#define paravirt_opptr_type "i"
> +#define PARAVIRT_CALL_POST  ""
> +#endif
> +
>  #define paravirt_type(op)				\
>  	[paravirt_typenum] "i" (PARAVIRT_PATCH(op)),	\
> -	[paravirt_opptr] "i" (&(pv_ops.op))
> +	[paravirt_opptr] paravirt_opptr_type (&(pv_ops.op))
>  #define paravirt_clobber(clobber)		\
>  	[paravirt_clobber] "i" (clobber)
>  
> @@ -379,9 +395,10 @@ int paravirt_disable_iospace(void);
>   * offset into the paravirt_patch_template structure, and can therefore be
>   * freely converted back into a structure offset.
>   */
> -#define PARAVIRT_CALL					\
> -	ANNOTATE_RETPOLINE_SAFE				\
> -	"call *%c[paravirt_opptr];"
> +#define PARAVIRT_CALL						\
> +	ANNOTATE_RETPOLINE_SAFE					\
> +	"call *%" paravirt_opptr_call "[paravirt_opptr];"	\
> +	PARAVIRT_CALL_POST

On Tue, Jul 30, 2019 at 12:12:44PM -0700, Thomas Garnier
wrote:
> These patches make some of the changes necessary to build the kernel as
> Position Independent Executable (PIE) on x86_64. Another patchset will
> add the PIE option and larger architecture changes.
Yeah, about this: do we have a longer writeup about the actual benefits
of all this and why we should take this all? After all, after looking
at the first couple of asm patches, it is posing restrictions to how
we deal with virtual addresses in asm (only RIP-relative addressing in
64-bit mode, MOVs with 64-bit immediates, etc, for example) and I'm
willing to bet money that some future unrelated change will break PIE
sooner or later. And I'd like to have a better justification why we
should enforce those new "rules" unconditionally.

Thx.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

On Tue, Aug 06, 2019 at 05:43:47PM +0200, Borislav Petkov
wrote:
> On Tue, Jul 30, 2019 at 12:12:44PM -0700, Thomas Garnier wrote:
> > These patches make some of the changes necessary to build the kernel
as
> > Position Independent Executable (PIE) on x86_64. Another patchset will
> > add the PIE option and larger architecture changes.
> 
> Yeah, about this: do we have a longer writeup about the actual benefits
> of all this and why we should take this all? After all, after looking
> at the first couple of asm patches, it is posing restrictions to how
> we deal with virtual addresses in asm (only RIP-relative addressing in
> 64-bit mode, MOVs with 64-bit immediates, etc, for example) and I'm
> willing to bet money that some future unrelated change will break PIE
> sooner or later.
Possibly objtool can help here; it should be possible to teach it about
these rules, and then it will yell when violated. That should avoid
regressions.

On Thu, Aug 29, 2019 at 12:55 PM Thomas Garnier <thgarnie at chromium.org>
wrote:
>
> On Tue, Aug 6, 2019 at 8:51 AM Peter Zijlstra <peterz at
infradead.org> wrote:
> >
> > On Tue, Aug 06, 2019 at 05:43:47PM +0200, Borislav Petkov wrote:
> > > On Tue, Jul 30, 2019 at 12:12:44PM -0700, Thomas Garnier wrote:
> > > > These patches make some of the changes necessary to build
the kernel as
> > > > Position Independent Executable (PIE) on x86_64. Another
patchset will
> > > > add the PIE option and larger architecture changes.
> > >
> > > Yeah, about this: do we have a longer writeup about the actual
benefits
> > > of all this and why we should take this all? After all, after
looking
> > > at the first couple of asm patches, it is posing restrictions to
how
> > > we deal with virtual addresses in asm (only RIP-relative
addressing in
> > > 64-bit mode, MOVs with 64-bit immediates, etc, for example) and
I'm
> > > willing to bet money that some future unrelated change will break
PIE
> > > sooner or later.
>
> The goal is being able to extend the range of addresses where the
> kernel can be placed with KASLR. I will look at clarifying that in the
> future.
>
> >
> > Possibly objtool can help here; it should be possible to teach it
about
> > these rules, and then it will yell when violated. That should avoid
> > regressions.
> >
>
> I will look into that as well.
Following a discussion with Kees. I will explore objtool in the
follow-up patchset as we still have more elaborate pie changes in the
second set. I like the idea overall and I think it would be great if
it works.