[PATCH 1/3] x86_64: further cleanup of 32-bit compat syscall mechanisms

[Jeremy Fitzhardinge]

AMD only supports "syscall" from 32-bit compat usermode.
Intel and Centaur(?) only support "sysenter" from 32-bit compat usermode.

Set the X86 feature bits accordingly, and set up the vdso in
accordance with those bits.  On the offchance we run on in a 64-bit
environment which supports neither syscall nor sysenter from 32-bit
mode, then fall back to the int $0x80 vdso.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
arch/x86/kernel/cpu/amd_64.c    |    2 ++
arch/x86/kernel/cpu/common_64.c |    3 ---
arch/x86/vdso/Makefile          |    2 +-
arch/x86/vdso/vdso32-setup.c    |   19 +++++++++----------
arch/x86/vdso/vdso32.S          |   13 ++++++++-----
arch/x86/xen/setup.c            |   10 +++++++---
include/asm-x86/vdso.h          |    8 ++++++++
7 files changed, 35 insertions(+), 22 deletions(-)

===================================================================
--- a/arch/x86/kernel/cpu/amd_64.c
+++ b/arch/x86/kernel/cpu/amd_64.c
@@ -115,6 +115,8 @@ static void __cpuinit early_init_amd(str
	/* c->x86_power is 8000_0007 edx. Bit 8 is constant TSC */
	if (c->x86_power & (1<<8))
		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
+
+	set_cpu_cap(c, X86_FEATURE_SYSCALL32);
}

static void __cpuinit init_amd(struct cpuinfo_x86 *c)
===================================================================
--- a/arch/x86/kernel/cpu/common_64.c
+++ b/arch/x86/kernel/cpu/common_64.c
@@ -315,9 +315,6 @@ static void __cpuinit early_identify_cpu
	if (c->extended_cpuid_level >= 0x80000007)
		c->x86_power = cpuid_edx(0x80000007);

-	/* Assume all 64-bit CPUs support 32-bit syscall */
-	set_cpu_cap(c, X86_FEATURE_SYSCALL32);
-
	if (c->x86_vendor != X86_VENDOR_UNKNOWN &&
	    cpu_devs[c->x86_vendor]->c_early_init)
		cpu_devs[c->x86_vendor]->c_early_init(c);
===================================================================
--- a/arch/x86/vdso/Makefile
+++ b/arch/x86/vdso/Makefile
@@ -62,7 +62,7 @@ endef
# Build multiple 32-bit vDSO images to choose from at boot time.
#
obj-$(VDSO32-y)			+= vdso32-syms.lds
-vdso32.so-$(CONFIG_X86_32)	+= int80
+vdso32.so-$(VDSO32-y)		+= int80
vdso32.so-$(CONFIG_COMPAT)	+= syscall
vdso32.so-$(VDSO32-y)		+= sysenter

===================================================================
--- a/arch/x86/vdso/vdso32-setup.c
+++ b/arch/x86/vdso/vdso32-setup.c
@@ -193,17 +193,12 @@ static __init void relocate_vdso(Elf32_E
	}
}

-/*
- * These symbols are defined by vdso32.S to mark the bounds
- * of the ELF DSO images included therein.
- */
-extern const char vdso32_default_start, vdso32_default_end;
-extern const char vdso32_sysenter_start, vdso32_sysenter_end;
static struct page *vdso32_pages[1];

#ifdef CONFIG_X86_64

#define	vdso32_sysenter()	(boot_cpu_has(X86_FEATURE_SYSENTER32))
+#define	vdso32_syscall()	(boot_cpu_has(X86_FEATURE_SYSCALL32))

/* May not be __init: called during resume */
void syscall32_cpu_init(void)
@@ -226,6 +221,7 @@ static inline void map_compat_vdso(int m
#else  /* CONFIG_X86_32 */

#define vdso32_sysenter()	(boot_cpu_has(X86_FEATURE_SEP))
+#define vdso32_syscall()	(0)

void enable_sep_cpu(void)
{
@@ -296,12 +292,15 @@ int __init sysenter_setup(void)
	gate_vma_init();
#endif

-	if (!vdso32_sysenter()) {
-		vsyscall = &vdso32_default_start;
-		vsyscall_len = &vdso32_default_end - &vdso32_default_start;
-	} else {
+	if (vdso32_syscall()) {
+		vsyscall = &vdso32_syscall_start;
+		vsyscall_len = &vdso32_syscall_end - &vdso32_syscall_start;
+	} else if (vdso32_sysenter()){
		vsyscall = &vdso32_sysenter_start;
		vsyscall_len = &vdso32_sysenter_end - &vdso32_sysenter_start;
+	} else {
+		vsyscall = &vdso32_int80_start;
+		vsyscall_len = &vdso32_int80_end - &vdso32_int80_start;
	}

	memcpy(syscall_page, vsyscall, vsyscall_len);
===================================================================
--- a/arch/x86/vdso/vdso32.S
+++ b/arch/x86/vdso/vdso32.S
@@ -2,14 +2,17 @@

__INITDATA

-	.globl vdso32_default_start, vdso32_default_end
-vdso32_default_start:
-#ifdef CONFIG_X86_32
+	.globl vdso32_int80_start, vdso32_int80_end
+vdso32_int80_start:
	.incbin "arch/x86/vdso/vdso32-int80.so"
-#else
+vdso32_int80_end:
+
+	.globl vdso32_syscall_start, vdso32_syscall_end
+vdso32_syscall_start:
+#ifdef CONFIG_COMPAT
	.incbin "arch/x86/vdso/vdso32-syscall.so"
#endif
-vdso32_default_end:
+vdso32_syscall_end:

	.globl vdso32_sysenter_start, vdso32_sysenter_end
vdso32_sysenter_start:
===================================================================
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -83,12 +83,16 @@ static void xen_idle(void)

/*
 * Set the bit indicating "nosegneg" library variants should be used.
+ * We only need to bother in pure 32-bit mode; compat 32-bit processes
+ * can have un-truncated segments, so wrapping around is allowed.
 */
static void __init fiddle_vdso(void)
{
-#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
-	extern const char vdso32_default_start;
-	u32 *mask = VDSO32_SYMBOL(&vdso32_default_start, NOTE_MASK);
+#ifdef CONFIG_X86_32
+	u32 *mask;
+	mask = VDSO32_SYMBOL(&vdso32_int80_start, NOTE_MASK);
+	*mask |= 1 << VDSO_NOTE_NONEGSEG_BIT;
+	mask = VDSO32_SYMBOL(&vdso32_sysenter_start, NOTE_MASK);
	*mask |= 1 << VDSO_NOTE_NONEGSEG_BIT;
#endif
}
===================================================================
--- a/include/asm-x86/vdso.h
+++ b/include/asm-x86/vdso.h
@@ -36,4 +36,12 @@ extern void __user __kernel_sigreturn;
extern void __user __kernel_sigreturn;
extern void __user __kernel_rt_sigreturn;

+/*
+ * These symbols are defined by vdso32.S to mark the bounds
+ * of the ELF DSO images included therein.
+ */
+extern const char vdso32_int80_start, vdso32_int80_end;
+extern const char vdso32_syscall_start, vdso32_syscall_end;
+extern const char vdso32_sysenter_start, vdso32_sysenter_end;
+
#endif	/* asm-x86/vdso.h */


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