lkml.org 
[lkml]   [2018]   [Jan]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 03/16] x86/entry/32: Leave the kernel via the trampoline stack
Date
From: Joerg Roedel <jroedel@suse.de>

Switch back to the trampoline stack before returning to
userspace.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/entry/entry_32.S | 58 ++++++++++++++++++++++++++++++++++++++++
arch/x86/kernel/asm-offsets_32.c | 1 +
2 files changed, 59 insertions(+)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 5a7bdb73be9f..14018eeb11c3 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -263,6 +263,61 @@
.endm

/*
+ * Switch back from the kernel stack to the entry stack.
+ *
+ * iret_frame > 0 adds code to copie over an iret frame from the old to
+ * the new stack. It also adds a check which bails out if
+ * we are not returning to user-space.
+ *
+ * This macro is allowed not modify eflags when iret_frame == 0.
+ */
+.macro SWITCH_TO_ENTRY_STACK iret_frame=0
+ .if \iret_frame > 0
+ /* Are we returning to userspace? */
+ testb $3, 4(%esp) /* return CS */
+ jz .Lend_\@
+ .endif
+
+ /*
+ * We run with user-%fs already loaded from pt_regs, so we don't
+ * have access to per_cpu data anymore, and there is no swapgs
+ * equivalent on x86_32.
+ * We work around this by loading the kernel-%fs again and
+ * reading the entry stack address from there. Then we restore
+ * the user-%fs and return.
+ */
+ pushl %fs
+ pushl %edi
+
+ /* Re-load kernel-%fs, after that we can use PER_CPU_VAR */
+ movl $(__KERNEL_PERCPU), %edi
+ movl %edi, %fs
+
+ /* Save old stack pointer to copy the return frame over if needed */
+ movl %esp, %edi
+ movl PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %esp
+
+ /* Now we are on the entry stack */
+
+ .if \iret_frame > 0
+ /* Stack frame: ss, esp, eflags, cs, eip, fs, edi */
+ pushl 6*4(%edi) /* ss */
+ pushl 5*4(%edi) /* esp */
+ pushl 4*4(%edi) /* eflags */
+ pushl 3*4(%edi) /* cs */
+ pushl 2*4(%edi) /* eip */
+ .endif
+
+ pushl 4(%edi) /* fs */
+
+ /* Restore user %edi and user %fs */
+ movl (%edi), %edi
+ popl %fs
+
+.Lend_\@:
+.endm
+
+/*
* %eax: prev task
* %edx: next task
*/
@@ -512,6 +567,8 @@ ENTRY(entry_SYSENTER_32)
btr $X86_EFLAGS_IF_BIT, (%esp)
popfl

+ SWITCH_TO_ENTRY_STACK
+
/*
* Return back to the vDSO, which will pop ecx and edx.
* Don't bother with DS and ES (they already contain __USER_DS).
@@ -601,6 +658,7 @@ restore_all:
.Lrestore_nocheck:
RESTORE_REGS 4 # skip orig_eax/error_code
.Lirq_return:
+ SWITCH_TO_ENTRY_STACK iret_frame=1
INTERRUPT_RETURN

.section .fixup, "ax"
diff --git a/arch/x86/kernel/asm-offsets_32.c b/arch/x86/kernel/asm-offsets_32.c
index 7270dd834f4b..b628f898edd2 100644
--- a/arch/x86/kernel/asm-offsets_32.c
+++ b/arch/x86/kernel/asm-offsets_32.c
@@ -50,6 +50,7 @@ void foo(void)
DEFINE(TSS_sysenter_stack, offsetof(struct cpu_entry_area, tss.x86_tss.sp1) -
offsetofend(struct cpu_entry_area, entry_stack_page.stack));

+ OFFSET(TSS_sp0, tss_struct, x86_tss.sp0);
OFFSET(TSS_sp1, tss_struct, x86_tss.sp1);

#ifdef CONFIG_CC_STACKPROTECTOR
--
2.13.6
\
 
 \ /
  Last update: 2018-01-16 17:56    [W:0.368 / U:1.324 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site