Merge compat and native code and clarify comments.
Signed-off-by: Brian Gerst <[email protected]>
---
arch/x86/entry/common.c | 48 +++++++++++++++-----------------
arch/x86/entry/entry_64_compat.S | 5 ++--
2 files changed, 24 insertions(+), 29 deletions(-)
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 4d7d6d25dda9..800664325542 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -241,34 +241,30 @@ __visible noinstr bool do_fast_syscall_32(struct pt_regs *regs)
if (!__do_fast_syscall_32(regs))
return false;
-#ifdef CONFIG_X86_64
/*
- * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
- * SYSRETL is available on all 64-bit CPUs, so we don't need to
- * bother with SYSEXIT.
- *
- * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
- * because the ECX fixup above will ensure that this is essentially
- * never the case.
+ * Check that the register state is valid for using SYSRETL/SYSEXIT
+ * to exit to userspace. Otherwise use the slower but fully capable
+ * IRET exit path.
*/
- return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
- regs->ip == landing_pad &&
- (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
-#else
- /*
- * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
- *
- * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
- * because the ECX fixup above will ensure that this is essentially
- * never the case.
- *
- * We don't allow syscalls at all from VM86 mode, but we still
- * need to check VM, because we might be returning from sys_vm86.
- */
- return regs->cs == __USER_CS && regs->ss == __USER_DS &&
- regs->ip == landing_pad &&
- (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
-#endif
+
+ /* XEN PV guests always use IRET path */
+ if (cpu_feature_enabled(X86_FEATURE_XENPV))
+ return false;
+
+ /* EIP must point to the VDSO landing pad */
+ if (unlikely(regs->ip != landing_pad))
+ return false;
+
+ /* CS and SS must match the values set in MSR_STAR */
+ if (unlikely(regs->cs != __USER32_CS || regs->ss != __USER_DS))
+ return false;
+
+ /* If the TF, RF, or VM flags are set, use IRET */
+ if (unlikely(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)))
+ return false;
+
+ /* Use SYSRETL/SYSEXIT to exit to userspace */
+ return true;
}
/* Returns true to return using SYSEXIT/SYSRETL, or false to use IRET */
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 27c05d08558a..84e21d1ebf10 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -211,9 +211,8 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
call do_fast_syscall_32
sysret32_from_system_call:
- /* XEN PV guests always use IRET path */
- ALTERNATIVE "testb %al, %al; jz swapgs_restore_regs_and_return_to_usermode", \
- "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
+ testb %al, %al /* Is SYSRET allowed? */
+ jz swapgs_restore_regs_and_return_to_usermode
/*
* Opportunistic SYSRET
--
2.41.0