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-rw-r--r--arch/x86/entry/common.c6
-rw-r--r--arch/x86/entry/entry_32.S7
-rw-r--r--arch/x86/entry/entry_64_compat.S20
-rw-r--r--arch/x86/entry/vdso/vdso32/system_call.S54
4 files changed, 61 insertions, 26 deletions
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index a89fdbc1f0be..03663740c866 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -421,7 +421,7 @@ __visible long do_fast_syscall_32(struct pt_regs *regs)
regs->ip = landing_pad;
/*
- * Fetch ECX from where the vDSO stashed it.
+ * Fetch EBP from where the vDSO stashed it.
*
* WARNING: We are in CONTEXT_USER and RCU isn't paying attention!
*/
@@ -432,10 +432,10 @@ __visible long do_fast_syscall_32(struct pt_regs *regs)
* Micro-optimization: the pointer we're following is explicitly
* 32 bits, so it can't be out of range.
*/
- __get_user(*(u32 *)&regs->cx,
+ __get_user(*(u32 *)&regs->bp,
(u32 __user __force *)(unsigned long)(u32)regs->sp)
#else
- get_user(*(u32 *)&regs->cx,
+ get_user(*(u32 *)&regs->bp,
(u32 __user __force *)(unsigned long)(u32)regs->sp)
#endif
) {
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 3eb572ed3d7a..f3b6d54e0042 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -292,7 +292,7 @@ ENTRY(entry_SYSENTER_32)
movl TSS_sysenter_sp0(%esp), %esp
sysenter_past_esp:
pushl $__USER_DS /* pt_regs->ss */
- pushl %ecx /* pt_regs->cx */
+ pushl %ebp /* pt_regs->sp (stashed in bp) */
pushfl /* pt_regs->flags (except IF = 0) */
orl $X86_EFLAGS_IF, (%esp) /* Fix IF */
pushl $__USER_CS /* pt_regs->cs */
@@ -308,8 +308,9 @@ sysenter_past_esp:
movl %esp, %eax
call do_fast_syscall_32
- testl %eax, %eax
- jz .Lsyscall_32_done
+ /* XEN PV guests always use IRET path */
+ ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+ "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
/* Opportunistic SYSEXIT */
TRACE_IRQS_ON /* User mode traces as IRQs on. */
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index c3201830a85e..6a1ae3751e82 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -63,7 +63,7 @@ ENTRY(entry_SYSENTER_compat)
/* Construct struct pt_regs on stack */
pushq $__USER32_DS /* pt_regs->ss */
- pushq %rcx /* pt_regs->sp */
+ pushq %rbp /* pt_regs->sp (stashed in bp) */
/*
* Push flags. This is nasty. First, interrupts are currently
@@ -82,14 +82,14 @@ ENTRY(entry_SYSENTER_compat)
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
pushq %rdx /* pt_regs->dx */
- pushq %rcx /* pt_regs->cx (will be overwritten) */
+ pushq %rcx /* pt_regs->cx */
pushq $-ENOSYS /* pt_regs->ax */
pushq %r8 /* pt_regs->r8 = 0 */
pushq %r8 /* pt_regs->r9 = 0 */
pushq %r8 /* pt_regs->r10 = 0 */
pushq %r8 /* pt_regs->r11 = 0 */
pushq %rbx /* pt_regs->rbx */
- pushq %rbp /* pt_regs->rbp */
+ pushq %rbp /* pt_regs->rbp (will be overwritten) */
pushq %r8 /* pt_regs->r12 = 0 */
pushq %r8 /* pt_regs->r13 = 0 */
pushq %r8 /* pt_regs->r14 = 0 */
@@ -121,8 +121,9 @@ sysenter_flags_fixed:
movq %rsp, %rdi
call do_fast_syscall_32
- testl %eax, %eax
- jz .Lsyscall_32_done
+ /* XEN PV guests always use IRET path */
+ ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+ "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
jmp sysret32_from_system_call
sysenter_fix_flags:
@@ -178,7 +179,7 @@ ENTRY(entry_SYSCALL_compat)
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
pushq %rdx /* pt_regs->dx */
- pushq %rcx /* pt_regs->cx (will be overwritten) */
+ pushq %rbp /* pt_regs->cx (stashed in bp) */
pushq $-ENOSYS /* pt_regs->ax */
xorq %r8,%r8
pushq %r8 /* pt_regs->r8 = 0 */
@@ -186,7 +187,7 @@ ENTRY(entry_SYSCALL_compat)
pushq %r8 /* pt_regs->r10 = 0 */
pushq %r8 /* pt_regs->r11 = 0 */
pushq %rbx /* pt_regs->rbx */
- pushq %rbp /* pt_regs->rbp */
+ pushq %rbp /* pt_regs->rbp (will be overwritten) */
pushq %r8 /* pt_regs->r12 = 0 */
pushq %r8 /* pt_regs->r13 = 0 */
pushq %r8 /* pt_regs->r14 = 0 */
@@ -200,8 +201,9 @@ ENTRY(entry_SYSCALL_compat)
movq %rsp, %rdi
call do_fast_syscall_32
- testl %eax, %eax
- jz .Lsyscall_32_done
+ /* XEN PV guests always use IRET path */
+ ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+ "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
/* Opportunistic SYSRET */
sysret32_from_system_call:
diff --git a/arch/x86/entry/vdso/vdso32/system_call.S b/arch/x86/entry/vdso/vdso32/system_call.S
index 93bd8452383f..3a1d9297074b 100644
--- a/arch/x86/entry/vdso/vdso32/system_call.S
+++ b/arch/x86/entry/vdso/vdso32/system_call.S
@@ -1,5 +1,5 @@
/*
- * Code for the vDSO. This version uses the old int $0x80 method.
+ * AT_SYSINFO entry point
*/
#include <asm/dwarf2.h>
@@ -21,35 +21,67 @@ __kernel_vsyscall:
/*
* Reshuffle regs so that all of any of the entry instructions
* will preserve enough state.
+ *
+ * A really nice entry sequence would be:
+ * pushl %edx
+ * pushl %ecx
+ * movl %esp, %ecx
+ *
+ * Unfortunately, naughty Android versions between July and December
+ * 2015 actually hardcode the traditional Linux SYSENTER entry
+ * sequence. That is severely broken for a number of reasons (ask
+ * anyone with an AMD CPU, for example). Nonetheless, we try to keep
+ * it working approximately as well as it ever worked.
+ *
+ * This link may eludicate some of the history:
+ * https://android-review.googlesource.com/#/q/Iac3295376d61ef83e713ac9b528f3b50aa780cd7
+ * personally, I find it hard to understand what's going on there.
+ *
+ * Note to future user developers: DO NOT USE SYSENTER IN YOUR CODE.
+ * Execute an indirect call to the address in the AT_SYSINFO auxv
+ * entry. That is the ONLY correct way to make a fast 32-bit system
+ * call on Linux. (Open-coding int $0x80 is also fine, but it's
+ * slow.)
*/
+ pushl %ecx
+ CFI_ADJUST_CFA_OFFSET 4
+ CFI_REL_OFFSET ecx, 0
pushl %edx
CFI_ADJUST_CFA_OFFSET 4
CFI_REL_OFFSET edx, 0
- pushl %ecx
+ pushl %ebp
CFI_ADJUST_CFA_OFFSET 4
- CFI_REL_OFFSET ecx, 0
- movl %esp, %ecx
+ CFI_REL_OFFSET ebp, 0
+
+ #define SYSENTER_SEQUENCE "movl %esp, %ebp; sysenter"
+ #define SYSCALL_SEQUENCE "movl %ecx, %ebp; syscall"
#ifdef CONFIG_X86_64
/* If SYSENTER (Intel) or SYSCALL32 (AMD) is available, use it. */
- ALTERNATIVE_2 "", "sysenter", X86_FEATURE_SYSENTER32, \
- "syscall", X86_FEATURE_SYSCALL32
+ ALTERNATIVE_2 "", SYSENTER_SEQUENCE, X86_FEATURE_SYSENTER32, \
+ SYSCALL_SEQUENCE, X86_FEATURE_SYSCALL32
#else
- ALTERNATIVE "", "sysenter", X86_FEATURE_SEP
+ ALTERNATIVE "", SYSENTER_SEQUENCE, X86_FEATURE_SEP
#endif
/* Enter using int $0x80 */
- movl (%esp), %ecx
int $0x80
GLOBAL(int80_landing_pad)
- /* Restore ECX and EDX in case they were clobbered. */
- popl %ecx
- CFI_RESTORE ecx
+ /*
+ * Restore EDX and ECX in case they were clobbered. EBP is not
+ * clobbered (the kernel restores it), but it's cleaner and
+ * probably faster to pop it than to adjust ESP using addl.
+ */
+ popl %ebp
+ CFI_RESTORE ebp
CFI_ADJUST_CFA_OFFSET -4
popl %edx
CFI_RESTORE edx
CFI_ADJUST_CFA_OFFSET -4
+ popl %ecx
+ CFI_RESTORE ecx
+ CFI_ADJUST_CFA_OFFSET -4
ret
CFI_ENDPROC
generated by cgit v1.2.3 (git 2.0.4) at 2024-06-23 11:14:42 +0000