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Subject[RFC 1/7] x86/asm/64: Allocate and enable the SYSENTER stack
Date
This will simplify some future code changes that will want some
temporary stack space in more places. It also lets us get rid of a
SWAPGS_UNSAFE_STACK user.

This does not depend on CONFIG_IA32_EMULATION because we'll want the
stack space even without IA32 emulation.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/entry/entry_64_compat.S | 2 +-
arch/x86/include/asm/processor.h | 3 ---
arch/x86/kernel/asm-offsets.c | 5 +++++
arch/x86/kernel/asm-offsets_32.c | 5 -----
arch/x86/kernel/cpu/common.c | 4 +++-
arch/x86/kernel/process.c | 2 --
arch/x86/kernel/traps.c | 3 +--
7 files changed, 10 insertions(+), 14 deletions(-)

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 932b96ce1b06..36c508c21480 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -47,7 +47,7 @@
*/
ENTRY(entry_SYSENTER_compat)
/* Interrupts are off on entry. */
- SWAPGS_UNSAFE_STACK
+ SWAPGS
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp

/*
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index f10dae14f951..0644f888b12c 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -338,14 +338,11 @@ struct tss_struct {
*/
unsigned long io_bitmap[IO_BITMAP_LONGS + 1];

-#ifdef CONFIG_X86_32
/*
* Space for the temporary SYSENTER stack.
*/
unsigned long SYSENTER_stack_canary;
unsigned long SYSENTER_stack[64];
-#endif
-
} ____cacheline_aligned;

DECLARE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss);
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index de827d6ac8c2..031bd35bd911 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -92,4 +92,9 @@ void common(void) {

BLANK();
DEFINE(PTREGS_SIZE, sizeof(struct pt_regs));
+
+ /* Offset from cpu_tss to SYSENTER_stack */
+ OFFSET(CPU_TSS_SYSENTER_stack, tss_struct, SYSENTER_stack);
+ /* Size of SYSENTER_stack */
+ DEFINE(SIZEOF_SYSENTER_stack, sizeof(((struct tss_struct *)0)->SYSENTER_stack));
}
diff --git a/arch/x86/kernel/asm-offsets_32.c b/arch/x86/kernel/asm-offsets_32.c
index 710edab9e644..6c683edf7015 100644
--- a/arch/x86/kernel/asm-offsets_32.c
+++ b/arch/x86/kernel/asm-offsets_32.c
@@ -49,11 +49,6 @@ void foo(void)
DEFINE(TSS_sysenter_sp0, offsetof(struct tss_struct, x86_tss.sp0) -
offsetofend(struct tss_struct, SYSENTER_stack));

- /* Offset from cpu_tss to SYSENTER_stack */
- OFFSET(CPU_TSS_SYSENTER_stack, tss_struct, SYSENTER_stack);
- /* Size of SYSENTER_stack */
- DEFINE(SIZEOF_SYSENTER_stack, sizeof(((struct tss_struct *)0)->SYSENTER_stack));
-
#ifdef CONFIG_CC_STACKPROTECTOR
BLANK();
OFFSET(stack_canary_offset, stack_canary, canary);
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index cdf79ab628c2..22f542170198 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1361,7 +1361,9 @@ void syscall_init(void)
* AMD doesn't allow SYSENTER in long mode (either 32- or 64-bit).
*/
wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)__KERNEL_CS);
- wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
+ wrmsrl_safe(MSR_IA32_SYSENTER_ESP,
+ (unsigned long)this_cpu_ptr(&cpu_tss) +
+ offsetofend(struct tss_struct, SYSENTER_stack));
wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
#else
wrmsrl(MSR_CSTAR, (unsigned long)ignore_sysret);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ff8a9acbcf8b..b49c78b73699 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -70,9 +70,7 @@ __visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss) = {
*/
.io_bitmap = { [0 ... IO_BITMAP_LONGS] = ~0 },
#endif
-#ifdef CONFIG_X86_32
.SYSENTER_stack_canary = STACK_END_MAGIC,
-#endif
};
EXPORT_PER_CPU_SYMBOL(cpu_tss);

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 42a9c4458f5d..01a9e25ee9d8 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -790,14 +790,13 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
debug_stack_usage_dec();

exit:
-#if defined(CONFIG_X86_32)
/*
* This is the most likely code path that involves non-trivial use
* of the SYSENTER stack. Check that we haven't overrun it.
*/
WARN(this_cpu_read(cpu_tss.SYSENTER_stack_canary) != STACK_END_MAGIC,
"Overran or corrupted SYSENTER stack\n");
-#endif
+
ist_exit(regs);
}
NOKPROBE_SYMBOL(do_debug);
--
2.13.6
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