On Wed, Jan 18, 2023 at 09:02:52PM +0100, Borislav Petkov wrote:
On Tue, Jan 17, 2023 at 04:04:22PM -0800, Luis Chamberlain wrote:
and now I'm seeing this while trying to build v5.1:
ld: arch/x86/boot/compressed/pgtable_64.o:(.bss+0x0): multiple definition of `__force_order'; arch/x86/boot/compressed/kaslr_64.o:(.bss+0x0): first defined here
You need to backport
aa5cacdc29d7 ("x86/asm: Replace __force_order with a memory clobber")
for that.
Happens when building older kernels with newer toolchain.
Thanks that certainly helps. FWIW if someone needs it, I had to remove the double colons on write cr0 and cr4 to compile, but this crashed :( Any ideas?
diff --git a/arch/x86/boot/compressed/kaslr_64.c b/arch/x86/boot/compressed/kaslr_64.c index 748456c365f4..9557c5a15b91 100644 --- a/arch/x86/boot/compressed/kaslr_64.c +++ b/arch/x86/boot/compressed/kaslr_64.c @@ -29,9 +29,6 @@ #define __PAGE_OFFSET __PAGE_OFFSET_BASE #include "../../mm/ident_map.c"
-/* Used by pgtable.h asm code to force instruction serialization. */ -unsigned long __force_order; - /* Used to track our page table allocation area. */ struct alloc_pgt_data { unsigned char *pgt_buf; diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c index f8debf7aeb4c..7471b48524cb 100644 --- a/arch/x86/boot/compressed/pgtable_64.c +++ b/arch/x86/boot/compressed/pgtable_64.c @@ -5,15 +5,6 @@ #include "pgtable.h" #include "../string.h"
-/* - * __force_order is used by special_insns.h asm code to force instruction - * serialization. - * - * It is not referenced from the code, but GCC < 5 with -fPIE would fail - * due to an undefined symbol. Define it to make these ancient GCCs work. - */ -unsigned long __force_order; - #define BIOS_START_MIN 0x20000U /* 128K, less than this is insane */ #define BIOS_START_MAX 0x9f000U /* 640K, absolute maximum */
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h index 0a3c4cab39db..5586e4cf62d3 100644 --- a/arch/x86/include/asm/special_insns.h +++ b/arch/x86/include/asm/special_insns.h @@ -7,49 +7,50 @@
#include <asm/nops.h>
+#define __FORCE_ORDER "m"(*(unsigned int *)0x1000UL) + /* - * Volatile isn't enough to prevent the compiler from reordering the - * read/write functions for the control registers and messing everything up. - * A memory clobber would solve the problem, but would prevent reordering of - * all loads stores around it, which can hurt performance. Solution is to - * use a variable and mimic reads and writes to it to enforce serialization + * The compiler should not reorder volatile asm statements with respect to each + * other: they should execute in program order. However GCC 4.9.x and 5.x have + * a bug (which was fixed in 8.1, 7.3 and 6.5) where they might reorder + * volatile asm. The write functions are not affected since they have memory + * clobbers preventing reordering. To prevent reads from being reordered with + * respect to writes, use a dummy memory operand */ -extern unsigned long __force_order; - static inline unsigned long native_read_cr0(void) { unsigned long val; - asm volatile("mov %%cr0,%0\n\t" : "=r" (val), "=m" (__force_order)); + asm volatile("mov %%cr0,%0\n\t" : "=r" (val) : __FORCE_ORDER); return val; }
static inline void native_write_cr0(unsigned long val) { - asm volatile("mov %0,%%cr0": : "r" (val), "m" (__force_order)); + asm volatile("mov %0,%%cr0": : "r" (val) : "memory"); }
static inline unsigned long native_read_cr2(void) { unsigned long val; - asm volatile("mov %%cr2,%0\n\t" : "=r" (val), "=m" (__force_order)); + asm volatile("mov %%cr2,%0\n\t" : "=r" (val) : __FORCE_ORDER); return val; }
static inline void native_write_cr2(unsigned long val) { - asm volatile("mov %0,%%cr2": : "r" (val), "m" (__force_order)); + asm volatile("mov %0,%%cr2": : "r" (val) : "memory"); }
static inline unsigned long __native_read_cr3(void) { unsigned long val; - asm volatile("mov %%cr3,%0\n\t" : "=r" (val), "=m" (__force_order)); + asm volatile("mov %%cr3,%0\n\t" : "=r" (val) : __FORCE_ORDER); return val; }
static inline void native_write_cr3(unsigned long val) { - asm volatile("mov %0,%%cr3": : "r" (val), "m" (__force_order)); + asm volatile("mov %0,%%cr3": : "r" (val) : "memory"); }
static inline unsigned long native_read_cr4(void) @@ -64,17 +65,17 @@ static inline unsigned long native_read_cr4(void) asm volatile("1: mov %%cr4, %0\n" "2:\n" _ASM_EXTABLE(1b, 2b) - : "=r" (val), "=m" (__force_order) : "0" (0)); + : "=r" (val) : "0" (0), __FORCE_ORDER); #else /* CR4 always exists on x86_64. */ - asm volatile("mov %%cr4,%0\n\t" : "=r" (val), "=m" (__force_order)); + asm volatile("mov %%cr4,%0\n\t" : "=r" (val) : __FORCE_ORDER); #endif return val; }
static inline void native_write_cr4(unsigned long val) { - asm volatile("mov %0,%%cr4": : "r" (val), "m" (__force_order)); + asm volatile("mov %0,%%cr4": : "r" (val) : "memory"); }
#ifdef CONFIG_X86_64