[tip: x86/fred] x86/fred: Let ret_from_fork_asm() jmp to asm_fred_exit_user when FRED is enabled

[tip-bot2 for H. Peter Anvin (Intel)]

The following commit has been merged into the x86/fred branch of tip:

Commit-ID:     51ef2a4da7ec347e3315af69a426ac36fab98a6c
Gitweb:        https://git.kernel.org/tip/51ef2a4da7ec347e3315af69a426ac36fab98a6c
Author:        H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
AuthorDate:    Tue, 05 Dec 2023 02:50:17 -08:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Wed, 31 Jan 2024 22:02:59 +01:00

x86/fred: Let ret_from_fork_asm() jmp to asm_fred_exit_user when FRED is enabled

Let ret_from_fork_asm() jmp to asm_fred_exit_user when FRED is enabled,
otherwise the existing IDT code is chosen.

Signed-off-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Link: https://lore.kernel.org/r/20231205105030.8698-29-xin3.li@xxxxxxxxx
---
 arch/x86/entry/entry_64.S      | 6 ++++++
 arch/x86/entry/entry_64_fred.S | 1 +
 2 files changed, 7 insertions(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 29ce68f..7c4b726 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -247,7 +247,13 @@ SYM_CODE_START(ret_from_fork_asm)
 	 * and unwind should work normally.
 	 */
 	UNWIND_HINT_REGS
+
+#ifdef CONFIG_X86_FRED
+	ALTERNATIVE "jmp swapgs_restore_regs_and_return_to_usermode", \
+		    "jmp asm_fred_exit_user", X86_FEATURE_FRED
+#else
 	jmp	swapgs_restore_regs_and_return_to_usermode
+#endif
 SYM_CODE_END(ret_from_fork_asm)
 .popsection
 
diff --git a/arch/x86/entry/entry_64_fred.S b/arch/x86/entry/entry_64_fred.S
index c1ddaf6..2271a1c 100644
--- a/arch/x86/entry/entry_64_fred.S
+++ b/arch/x86/entry/entry_64_fred.S
@@ -32,6 +32,7 @@
 SYM_CODE_START_NOALIGN(asm_fred_entrypoint_user)
 	FRED_ENTER
 	call	fred_entry_from_user
+SYM_INNER_LABEL(asm_fred_exit_user, SYM_L_GLOBAL)
 	FRED_EXIT
 	ERETU
 SYM_CODE_END(asm_fred_entrypoint_user)