[tip:x86/asm] x86/head: Pass a real pt_regs and trapnr to early_fixup_exception()

From: tip-bot for Andy Lutomirski
Date: Wed Apr 13 2016 - 07:45:35 EST

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Commit-ID: 7bbcdb1ca4d2fd69094ee89c18601b396531ca9f
Gitweb: http://git.kernel.org/tip/7bbcdb1ca4d2fd69094ee89c18601b396531ca9f
Author: Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Sat, 2 Apr 2016 07:01:32 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 13 Apr 2016 11:37:44 +0200

x86/head: Pass a real pt_regs and trapnr to early_fixup_exception()

early_fixup_exception() is limited by the fact that it doesn't have a
real struct pt_regs. Change both the 32-bit and 64-bit asm and the
C code to pass and accept a real pt_regs.

Tested-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Acked-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: KVM list <kvm@xxxxxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: xen-devel <Xen-devel@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/e3fb680fcfd5e23e38237e8328b64a25cc121d37.1459605520.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/include/asm/uaccess.h | 2 +-
arch/x86/kernel/head_32.S | 74 +++++++++++++++++++++++++++++-------------
arch/x86/kernel/head_64.S | 68 ++++++++++++++++++++------------------
arch/x86/mm/extable.c | 6 ++--
4 files changed, 92 insertions(+), 58 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index a969ae6..b6fb311 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -110,7 +110,7 @@ struct exception_table_entry {

extern int fixup_exception(struct pt_regs *regs, int trapnr);
extern bool ex_has_fault_handler(unsigned long ip);
-extern int early_fixup_exception(unsigned long *ip);
+extern int early_fixup_exception(struct pt_regs *regs, int trapnr);

/*
* These are the main single-value transfer routines. They automatically
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 54cdbd2..0904536 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -568,29 +568,64 @@ early_idt_handler_common:
je hlt_loop
incl %ss:early_recursion_flag

- push %eax # 16(%esp)
- push %ecx # 12(%esp)
- push %edx # 8(%esp)
- push %ds # 4(%esp)
- push %es # 0(%esp)
- movl $(__KERNEL_DS),%eax
- movl %eax,%ds
- movl %eax,%es
+ /* The vector number is in pt_regs->gs */

- cmpl $(__KERNEL_CS),32(%esp)
+ cld
+ pushl %fs /* pt_regs->fs */
+ movw $0, 2(%esp) /* clear high bits (some CPUs leave garbage) */
+ pushl %es /* pt_regs->es */
+ movw $0, 2(%esp) /* clear high bits (some CPUs leave garbage) */
+ pushl %ds /* pt_regs->ds */
+ movw $0, 2(%esp) /* clear high bits (some CPUs leave garbage) */
+ pushl %eax /* pt_regs->ax */
+ pushl %ebp /* pt_regs->bp */
+ pushl %edi /* pt_regs->di */
+ pushl %esi /* pt_regs->si */
+ pushl %edx /* pt_regs->dx */
+ pushl %ecx /* pt_regs->cx */
+ pushl %ebx /* pt_regs->bx */
+
+ /* Fix up DS and ES */
+ movl $(__KERNEL_DS), %ecx
+ movl %ecx, %ds
+ movl %ecx, %es
+
+ /* Load the vector number into EDX */
+ movl PT_GS(%esp), %edx
+
+ /* Load GS into pt_regs->gs and clear high bits */
+ movw %gs, PT_GS(%esp)
+ movw $0, PT_GS+2(%esp)
+
+ cmpl $(__KERNEL_CS),PT_CS(%esp)
jne 10f

- leal 28(%esp),%eax # Pointer to %eip
- call early_fixup_exception
- andl %eax,%eax
- jnz ex_entry /* found an exception entry */
+ movl %esp, %eax /* args are pt_regs (EAX), trapnr (EDX) */
+ call early_fixup_exception
+ andl %eax,%eax
+ jz 10f /* Exception wasn't fixed up */
+
+ popl %ebx /* pt_regs->bx */
+ popl %ecx /* pt_regs->cx */
+ popl %edx /* pt_regs->dx */
+ popl %esi /* pt_regs->si */
+ popl %edi /* pt_regs->di */
+ popl %ebp /* pt_regs->bp */
+ popl %eax /* pt_regs->ax */
+ popl %ds /* pt_regs->ds */
+ popl %es /* pt_regs->es */
+ popl %fs /* pt_regs->fs */
+ popl %gs /* pt_regs->gs */
+ decl %ss:early_recursion_flag
+ addl $4, %esp /* pop pt_regs->orig_ax */
+ iret

10:
#ifdef CONFIG_PRINTK
xorl %eax,%eax
- movw %ax,2(%esp) /* clean up the segment values on some cpus */
- movw %ax,6(%esp)
- movw %ax,34(%esp)
+ movw %ax,PT_FS+2(%esp) /* clean up the segment values on some cpus */
+ movw %ax,PT_DS+2(%esp)
+ movw %ax,PT_ES+2(%esp)
leal 40(%esp),%eax
pushl %eax /* %esp before the exception */
pushl %ebx
@@ -608,13 +643,6 @@ hlt_loop:
hlt
jmp hlt_loop

-ex_entry:
- pop %es
- pop %ds
- pop %edx
- pop %ecx
- pop %eax
- decl %ss:early_recursion_flag
.Lis_nmi:
addl $8,%esp /* drop vector number and error code */
iret
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 22fbf9d..9e8636d 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -20,6 +20,7 @@
#include <asm/processor-flags.h>
#include <asm/percpu.h>
#include <asm/nops.h>
+#include "../entry/calling.h"

#ifdef CONFIG_PARAVIRT
#include <asm/asm-offsets.h>
@@ -357,39 +358,52 @@ early_idt_handler_common:
jz 1f
incl early_recursion_flag(%rip)

- pushq %rax # 64(%rsp)
- pushq %rcx # 56(%rsp)
- pushq %rdx # 48(%rsp)
- pushq %rsi # 40(%rsp)
- pushq %rdi # 32(%rsp)
- pushq %r8 # 24(%rsp)
- pushq %r9 # 16(%rsp)
- pushq %r10 # 8(%rsp)
- pushq %r11 # 0(%rsp)
-
- cmpl $__KERNEL_CS,96(%rsp)
+ /* The vector number is currently in the pt_regs->di slot. */
+ pushq %rsi /* pt_regs->si */
+ movq 8(%rsp), %rsi /* RSI = vector number */
+ movq %rdi, 8(%rsp) /* pt_regs->di = RDI */
+ pushq %rdx /* pt_regs->dx */
+ pushq %rcx /* pt_regs->cx */
+ pushq %rax /* pt_regs->ax */
+ pushq %r8 /* pt_regs->r8 */
+ pushq %r9 /* pt_regs->r9 */
+ pushq %r10 /* pt_regs->r10 */
+ pushq %r11 /* pt_regs->r11 */
+ pushq %rbx /* pt_regs->bx */
+ pushq %rbp /* pt_regs->bp */
+ pushq %r12 /* pt_regs->r12 */
+ pushq %r13 /* pt_regs->r13 */
+ pushq %r14 /* pt_regs->r14 */
+ pushq %r15 /* pt_regs->r15 */
+
+ cmpl $__KERNEL_CS,CS(%rsp)
jne 11f

- cmpl $14,72(%rsp) # Page fault?
+ cmpq $14,%rsi /* Page fault? */
jnz 10f
- GET_CR2_INTO(%rdi) # can clobber any volatile register if pv
+ GET_CR2_INTO(%rdi) /* Can clobber any volatile register if pv */
call early_make_pgtable
andl %eax,%eax
- jz 20f # All good
+ jz 20f /* All good */

10:
- leaq 88(%rsp),%rdi # Pointer to %rip
+ movq %rsp,%rdi /* RDI = pt_regs; RSI is already trapnr */
call early_fixup_exception
andl %eax,%eax
jnz 20f # Found an exception entry

11:
#ifdef CONFIG_EARLY_PRINTK
- GET_CR2_INTO(%r9) # can clobber any volatile register if pv
- movl 80(%rsp),%r8d # error code
- movl 72(%rsp),%esi # vector number
- movl 96(%rsp),%edx # %cs
- movq 88(%rsp),%rcx # %rip
+ /*
+ * On paravirt kernels, GET_CR2_INTO clobbers callee-clobbered regs.
+ * We only care about RSI, so we need to save it.
+ */
+ movq %rsi,%rbx /* Save vector number */
+ GET_CR2_INTO(%r9)
+ movq ORIG_RAX(%rsp),%r8 /* error code */
+ movq %rbx,%rsi /* vector number */
+ movq CS(%rsp),%rdx
+ movq RIP(%rsp),%rcx
xorl %eax,%eax
leaq early_idt_msg(%rip),%rdi
call early_printk
@@ -398,24 +412,16 @@ early_idt_handler_common:
call dump_stack
#ifdef CONFIG_KALLSYMS
leaq early_idt_ripmsg(%rip),%rdi
- movq 40(%rsp),%rsi # %rip again
+ movq RIP(%rsp),%rsi # %rip again
call __print_symbol
#endif
#endif /* EARLY_PRINTK */
1: hlt
jmp 1b

-20: # Exception table entry found or page table generated
- popq %r11
- popq %r10
- popq %r9
- popq %r8
- popq %rdi
- popq %rsi
- popq %rdx
- popq %rcx
- popq %rax
+20: /* Exception table entry found or page table generated */
decl early_recursion_flag(%rip)
+ jmp restore_regs_and_iret
.Lis_nmi:
addq $16,%rsp # drop vector number and error code
INTERRUPT_RETURN
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 82447b3..1366e06 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -83,13 +83,13 @@ int fixup_exception(struct pt_regs *regs, int trapnr)
}

/* Restricted version used during very early boot */
-int __init early_fixup_exception(unsigned long *ip)
+int __init early_fixup_exception(struct pt_regs *regs, int trapnr)
{
const struct exception_table_entry *e;
unsigned long new_ip;
ex_handler_t handler;

- e = search_exception_tables(*ip);
+ e = search_exception_tables(regs->ip);
if (!e)
return 0;

@@ -100,6 +100,6 @@ int __init early_fixup_exception(unsigned long *ip)
if (handler != ex_handler_default)
return 0;

- *ip = new_ip;
+ regs->ip = new_ip;
return 1;
}

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