From: Borislav Petkov <bp@alien8.de>
To: "H. Peter Anvin" <hpa@zytor.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
the arch/x86 maintainers <x86@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
Andi Kleen <ak@linux.intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Andy Lutomirski <luto@amacapital.net>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC, PATCHv1 15/28] x86: detect 5-level paging support
Date: Thu, 15 Dec 2016 15:39:44 +0100 [thread overview]
Message-ID: <20161215143944.ruxr6r3b2atg4tnf@pd.tnic> (raw)
Message-ID: <20161215143944.6ewS7M75bFSSMbUIA-zV5lgy3no7NUwNX8HL836bC8Q@z> (raw)
In-Reply-To: <BD4BD1C9-F6FD-4905-9B09-059284FD2713@alien8.de>
On Wed, Dec 14, 2016 at 12:07:54AM +0100, Boris Petkov wrote:
> Thus I was thinking of adding a build-time check for the gcc version
> but that might turn out to be more code in the end than those ugly
> ifnc clauses.
IOW, something like this. I did this just to try to see whether it is
doable. And it does work - gcc 4.8 and 4.9 -m32 cannot preserve the PIC
register - actually the inline asm fails building due to impossible
constraints.
However, so many lines changed just to save the ifnc, meh, I dunno...
---
arch/x86/boot/compressed/Makefile | 8 ++++++
arch/x86/boot/cpuflags.c | 14 ++++++++--
scripts/gcc-clobber-pic.sh | 58 +++++++++++++++++++++++++++++++++++++++
3 files changed, 77 insertions(+), 3 deletions(-)
create mode 100755 scripts/gcc-clobber-pic.sh
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 34d9e15857c3..705fc2ab3fd6 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -35,6 +35,14 @@ KBUILD_CFLAGS += -mno-mmx -mno-sse
KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
+# check whether inline asm clobbers the PIC register
+ifeq ($(CONFIG_X86_32),y)
+ifeq ($(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-clobber-pic.sh $(CC) -m32),n)
+ KBUILD_CFLAGS += -DCC_PRESERVES_PIC
+ KBUILD_AFLAGS += -DCC_PRESERVES_PIC
+endif
+endif
+
KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
GCOV_PROFILE := n
UBSAN_SANITIZE :=n
diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
index 6687ab953257..913c3f5ab3a0 100644
--- a/arch/x86/boot/cpuflags.c
+++ b/arch/x86/boot/cpuflags.c
@@ -70,11 +70,19 @@ int has_eflag(unsigned long mask)
# define EBX_REG "=b"
#endif
+#if defined(__i386__) && defined(__PIC__) && !defined(CC_PRESERVES_PIC)
+# define SAVE_PIC ".ifnc %%ebx, %3; movl %%ebx, %3; .endif\n\t"
+# define SWAP_PIC ".ifnc %%ebx, %3; xchgl %%ebx, %3; .endif\n\t"
+#else
+# define SAVE_PIC
+# define SWAP_PIC
+#endif
+
static inline void cpuid(u32 id, u32 *a, u32 *b, u32 *c, u32 *d)
{
- asm volatile(".ifnc %%ebx,%3 ; movl %%ebx,%3 ; .endif \n\t"
- "cpuid \n\t"
- ".ifnc %%ebx,%3 ; xchgl %%ebx,%3 ; .endif \n\t"
+ asm volatile(SAVE_PIC
+ "cpuid\n\t"
+ SWAP_PIC
: "=a" (*a), "=c" (*c), "=d" (*d), EBX_REG (*b)
: "a" (id)
);
diff --git a/scripts/gcc-clobber-pic.sh b/scripts/gcc-clobber-pic.sh
new file mode 100755
index 000000000000..7ff10edf9b08
--- /dev/null
+++ b/scripts/gcc-clobber-pic.sh
@@ -0,0 +1,58 @@
+#!/bin/bash -x
+err=0
+O=$(mktemp)
+cat << "END" | $@ -fPIC -x c - -o $O >/dev/null 2>&1 || err=1
+int some_global_var, some_other_global_var;
+
+typedef unsigned int u32;
+
+void __attribute__((noinline)) foo(void)
+{
+ asm volatile("# some crap just so that we don't get optimized away");
+
+ some_other_global_var = 43;
+}
+
+static inline void cpuid(u32 id, u32 *a, u32 *b, u32 *c, u32 *d)
+{
+ asm volatile("cpuid"
+ : "=a" (*a), "=b" (*b), "=c" (*c), "=d" (*d)
+ : "a" (id), "2" (*c)
+ : "si", "di"
+ );
+
+ some_global_var = 42;
+ foo();
+}
+
+int main(void)
+{
+ u32 a, b, c = 0, d;
+
+ cpuid(0x1, &a, &b, &c, &d);
+
+ /*
+ * Make sure foo() gets actually called and not optimized away due to
+ * miscompilation.
+ */
+ if (some_global_var == 42 && some_other_global_var == 43)
+ return 0;
+ else
+ return 1;
+}
+END
+
+if (( $err ));
+then
+ exit 1
+fi
+
+chmod u+x $O
+$O
+
+if ! (( $? ));
+then
+ echo "n"
+fi
+
+rm -f $O
--
2.11.0
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
next prev parent reply other threads:[~2016-12-15 14:39 UTC|newest]
Thread overview: 113+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-08 16:21 [RFC, PATCHv1 00/28] 5-level paging Kirill A. Shutemov
2016-12-08 16:21 ` [QEMU, PATCH] x86: implement la57 paging mode Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:48 ` [Qemu-devel] " no-reply
2016-12-08 16:48 ` no-reply
2016-12-08 16:21 ` [RFC, PATCHv1 01/28] asm-generic: introduce 5level-fixup.h Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 02/28] asm-generic: introduce __ARCH_USE_5LEVEL_HACK Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 03/28] arch, mm: convert all architectures to use 5level-fixup.h Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 04/28] asm-generic: introduce <asm-generic/pgtable-nop4d.h> Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 05/28] mm: convert generic code to 5-level paging Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 06/28] x86: basic changes into headers for " Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 07/28] x86: trivial portion of 5-level paging conversion Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 08/28] x86/gup: add 5-level paging support Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 09/28] x86/ident_map: " Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 10/28] x86/mm: add support of p4d_t in vmalloc_fault() Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 11/28] x86/power: support p4d_t in hibernate code Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 12/28] x86/kexec: support p4d_t Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 13/28] x86: convert the rest of the code to " Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 14/28] mm: introduce __p4d_alloc() Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 15/28] x86: detect 5-level paging support Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 20:05 ` Borislav Petkov
2016-12-08 20:08 ` Linus Torvalds
2016-12-08 20:08 ` Linus Torvalds
2016-12-08 20:20 ` Borislav Petkov
2016-12-13 22:44 ` H. Peter Anvin
2016-12-13 22:44 ` H. Peter Anvin
2016-12-13 23:07 ` Boris Petkov
2016-12-13 23:07 ` Boris Petkov
2016-12-15 14:39 ` Borislav Petkov [this message]
2016-12-15 14:39 ` Borislav Petkov
2016-12-15 17:52 ` hpa
2016-12-15 17:52 ` hpa
2016-12-15 19:09 ` Borislav Petkov
2016-12-15 19:20 ` Andi Kleen
2016-12-15 19:20 ` Andi Kleen
2016-12-15 20:52 ` hpa
2016-12-15 20:52 ` hpa
2016-12-15 20:57 ` hpa
2016-12-15 20:57 ` hpa
2016-12-09 15:32 ` Kirill A. Shutemov
2016-12-09 16:33 ` Borislav Petkov
2016-12-13 22:50 ` H. Peter Anvin
2016-12-13 22:50 ` H. Peter Anvin
2016-12-08 16:21 ` [RFC, PATCHv1 16/28] x86/asm: remove __VIRTUAL_MASK_SHIFT==47 assert Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 18:39 ` Andy Lutomirski
2016-12-08 19:22 ` Kirill A. Shutemov
2016-12-08 19:22 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 17/28] x86/mm: define virtual memory map for 5-level paging Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 18:56 ` Randy Dunlap
2016-12-08 19:24 ` Kirill A. Shutemov
2016-12-08 19:24 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 18/28] x86/paravirt: make paravirt code support " Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 19/28] x86/mm: basic defines/helpers for CONFIG_X86_5LEVEL Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 20/28] x86/dump_pagetables: support 5-level paging Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 21/28] x86/mm: extend kasan to " Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 22/28] x86/espfix: " Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 18:40 ` Andy Lutomirski
2016-12-08 18:40 ` Andy Lutomirski
2016-12-12 14:22 ` Kirill A. Shutemov
2016-12-12 14:22 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 23/28] x86/mm: add support of additional page table level during early boot Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 24/28] x86/mm: add sync_global_pgds() for configuration with 5-level paging Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 18:42 ` Andy Lutomirski
2016-12-08 19:33 ` Kirill A. Shutemov
2016-12-08 19:33 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 25/28] x86/mm: make kernel_physical_mapping_init() support " Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 26/28] x86/mm: add support for 5-level paging for KASLR Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 27/28] x86: enable la57 support Kirill A. Shutemov
2016-12-08 16:21 ` Kirill A. Shutemov
2016-12-08 16:21 ` [RFC, PATCHv1 28/28] TESTING-ONLY: bump TASK_SIZE_MAX Kirill A. Shutemov
2016-12-08 18:16 ` [RFC, PATCHv1 00/28] 5-level paging Linus Torvalds
2016-12-08 18:16 ` Linus Torvalds
2016-12-08 18:26 ` hpa
2016-12-08 18:26 ` hpa
2016-12-08 19:20 ` Kirill A. Shutemov
2016-12-08 19:20 ` Kirill A. Shutemov
2016-12-09 5:01 ` Ingo Molnar
2016-12-09 5:01 ` Ingo Molnar
2016-12-09 10:24 ` Arnd Bergmann
2016-12-09 10:51 ` Catalin Marinas
2016-12-09 10:51 ` Catalin Marinas
2016-12-09 10:37 ` Kirill A. Shutemov
2016-12-09 10:37 ` Kirill A. Shutemov
2016-12-09 16:40 ` Andi Kleen
2016-12-09 17:21 ` Kirill A. Shutemov
2016-12-09 17:21 ` Kirill A. Shutemov
2016-12-09 16:49 ` Dave Hansen
2016-12-09 16:49 ` Dave Hansen
2016-12-13 21:06 ` Dave Hansen
2016-12-13 21:06 ` Dave Hansen
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