kernel/x86: add ability to set GS segment base from userland

Needed for Wine.

Co-authored-by: Jérôme Duval <[email protected]>

Change-Id: I13f6a5802fce04fd2ebb4cc01ecd2f12c90830db
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4839
Reviewed-by: Jérôme Duval <[email protected]>
Reviewed-by: X512 <[email protected]>
Reviewed-by: Fredrik Holmqvist <[email protected]>
Reviewed-by: waddlesplash <[email protected]>
Tested-by: Commit checker robot <[email protected]>

headers/private/kernel/arch/x86/arch_thread_types.h

@@ -48,6 +48,8 @@ struct arch_thread {
 
 	uintptr_t*		current_stack;
 	uintptr_t		instruction_pointer;
+
+	uint64			user_gs_base;
 #else
 	struct farcall	current_stack;
 	struct farcall	interrupt_stack;

headers/private/system/arch/x86/arch_thread_defs.h

@@ -0,0 +1,13 @@
+/*
+ * Copyright 2022, The Haiku Team. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _X86_THREAD_DEFS_H
+#define _X86_THREAD_DEFS_H
+
+
+#define THREAD_SYSCALLS			"thread"
+#define THREAD_SET_GS_BASE		1
+
+
+#endif	/* _X86_THREAD_DEFS_H */

src/system/kernel/arch/x86/64/thread.cpp

@@ -13,9 +13,11 @@
 
 #include <string.h>
 
+#include <arch_thread_defs.h>
 #include <commpage.h>
 #include <cpu.h>
 #include <debug.h>
+#include <generic_syscall.h>
 #include <kernel.h>
 #include <ksignal.h>
 #include <int.h>
@@ -96,6 +98,7 @@ x86_set_tls_context(Thread* thread)
 {
 	// Set FS segment base address to the TLS segment.
 	x86_write_msr(IA32_MSR_FS_BASE, thread->user_local_storage);
+	x86_write_msr(IA32_MSR_KERNEL_GS_BASE, thread->arch_info.user_gs_base);
 }
 
 
@@ -135,6 +138,32 @@ get_signal_stack(Thread* thread, iframe* frame, struct sigaction* action,
 }
 
 
+static status_t
+arch_thread_control(const char* subsystem, uint32 function, void* buffer,
+	size_t bufferSize)
+{
+	switch (function) {
+		case THREAD_SET_GS_BASE:
+		{
+			uint64 base;
+			if (bufferSize != sizeof(base))
+				return B_BAD_VALUE;
+
+			if (!IS_USER_ADDRESS(buffer)
+				|| user_memcpy(&base, buffer, sizeof(base)) < B_OK) {
+				return B_BAD_ADDRESS;
+			}
+
+			Thread* thread = thread_get_current_thread();
+			thread->arch_info.user_gs_base = base;
+			x86_write_msr(IA32_MSR_KERNEL_GS_BASE, base);
+			return B_OK;
+		}
+	}
+	return B_BAD_HANDLER;
+}
+
+
 //	#pragma mark -
 
 
@@ -172,6 +201,9 @@ arch_thread_init(kernel_args* args)
 			"fxsaveq %0"
 			:: "m" (sInitialState.fpu_state));
 	}
+
+	register_generic_syscall(THREAD_SYSCALLS, arch_thread_control, 1, 0);
+
 	return B_OK;
 }
 

src/system/kernel/arch/x86/Jamfile

@@ -11,6 +11,7 @@ SubDirHdrs $(SUBDIR) timers ;
 
 UsePrivateKernelHeaders ;
 UsePrivateHeaders shared ;
+UsePrivateHeaders [ FDirName system arch x86 ] ;
 
 SEARCH_SOURCE += [ FDirName $(SUBDIR) paging ] ;
 SEARCH_SOURCE += [ FDirName $(SUBDIR) timers ] ;