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Date: Fri, 16 Oct 2015 15:42:54 -0700
From: Andy Lutomirski <luto@...nel.org>
To: x86@...nel.org, linux-kernel@...r.kernel.org
Cc: Brian Gerst <brgerst@...il.com>,
Denys Vlasenko <dvlasenk@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v2 1/2] x86/entry/32: Fix entry_INT80_32 to expect interrupts to be on
When I rewrote entry_INT80_32, I thought that int80 was an interrupt
gate. It's a trap gate. *facepalm*
Thanks to Brian Gerst for pointing out that it's better to change
the entry code than to change the gate type.
Suggested-by: Brian Gerst <brgerst@...il.com>
Reported-by: Borislav Petkov <bp@...e.de>
Fixes: 150ac78d63af ("x86/entry/32: Switch INT80 to the new C syscall path")
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
arch/x86/entry/common.c | 15 ++++++++++++---
arch/x86/entry/entry_32.S | 8 ++++----
arch/x86/entry/entry_64_compat.S | 2 +-
3 files changed, 17 insertions(+), 8 deletions(-)
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index b53e04d301a3..09afb3b6acbb 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -351,7 +351,14 @@ __visible inline void syscall_return_slowpath(struct pt_regs *regs)
* in workloads that use it, and it's usually called from
* do_fast_syscall_32, so forcibly inline it to improve performance.
*/
-static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
+#ifdef CONFIG_X86_32
+/* 32-bit kernels use a trap gate for int80, and the asm code calls here. */
+__visible
+#else
+/* 64-bit kernels use do_syscall_32_irqs_off instead. */
+static
+#endif
+__always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
{
struct thread_info *ti = pt_regs_to_thread_info(regs);
unsigned int nr = (unsigned int)regs->orig_ax;
@@ -386,12 +393,14 @@ static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
syscall_return_slowpath(regs);
}
-/* Handles int $0x80 */
-__visible void do_int80_syscall_32(struct pt_regs *regs)
+#ifdef CONFIG_X86_64
+/* Handles int $0x80 on 64-bit kernels */
+__visible void do_syscall_32_irqs_off(struct pt_regs *regs)
{
local_irq_enable();
do_syscall_32_irqs_on(regs);
}
+#endif
/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
__visible long do_fast_syscall_32(struct pt_regs *regs)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 07a041b91af1..ba0dad937be9 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -346,13 +346,13 @@ ENTRY(entry_INT80_32)
SAVE_ALL pt_regs_ax=$-ENOSYS /* save rest */
/*
- * User mode is traced as though IRQs are on, and the interrupt gate
- * turned them off.
+ * User mode is traced as though IRQs are on. Unlike the 64-bit
+ * case, int80 is a trap gate on 32-bit kernels, so interrupts
+ * are already on (unless user code is messing around with iopl).
*/
- TRACE_IRQS_OFF
movl %esp, %eax
- call do_int80_syscall_32
+ call do_syscall_32_irqs_on
.Lsyscall_32_done:
restore_all:
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 78becafe60d1..dd160e4e2ef5 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -303,7 +303,7 @@ ENTRY(entry_INT80_compat)
TRACE_IRQS_OFF
movq %rsp, %rdi
- call do_int80_syscall_32
+ call do_syscall_32_irqs_off
.Lsyscall_32_done:
/* Go back to user mode. */
--
2.4.3
--
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