git: 0f44d9df994b - stable/14 - amd64: do not handle fs/gs bases conditionally on the selector

The branch stable/14 has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=0f44d9df994b398ba4591141559da6db18fff557

commit 0f44d9df994b398ba4591141559da6db18fff557
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2025-05-19 01:30:14 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2025-06-12 18:02:49 +0000

    amd64: do not handle fs/gs bases conditionally on the selector
    
    (cherry picked from commit ddab534cd6f6557740c24ff2019642880ad8bef6)
---
 sys/amd64/amd64/cpu_switch.S    |  6 ------
 sys/amd64/amd64/exception.S     | 29 -----------------------------
 sys/amd64/amd64/machdep.c       |  6 ++----
 sys/amd64/ia32/ia32_exception.S |  3 +--
 4 files changed, 3 insertions(+), 41 deletions(-)

diff --git a/sys/amd64/amd64/cpu_switch.S b/sys/amd64/amd64/cpu_switch.S
index 2a3eced01ab3..2a829c7507ea 100644
--- a/sys/amd64/amd64/cpu_switch.S
+++ b/sys/amd64/amd64/cpu_switch.S
@@ -91,14 +91,8 @@ ENTRY(cpu_switch)
 	jnz	2f
 	testb	$CPUID_STDEXT_FSGSBASE,cpu_stdext_feature(%rip)
 	jz	2f
-	movl	%fs,%eax
-	cmpl	$KUF32SEL,%eax
-	jne	1f
 	rdfsbase %rax
 	movq	%rax,PCB_FSBASE(%r8)
-1:	movl	%gs,%eax
-	cmpl	$KUG32SEL,%eax
-	jne	2f
 	movq	%rdx,%r12
 	movl	$MSR_KGSBASE,%ecx		/* Read user gs base */
 	rdmsr
diff --git a/sys/amd64/amd64/exception.S b/sys/amd64/amd64/exception.S
index 90f7a88f5d52..797b2fe748f3 100644
--- a/sys/amd64/amd64/exception.S
+++ b/sys/amd64/amd64/exception.S
@@ -479,22 +479,14 @@ prot_addrf:
 	jz	6f			/* already running with kernel GS.base */
 	testb	$CPUID_STDEXT_FSGSBASE,cpu_stdext_feature(%rip)
 	jz	2f
-	cmpw	$KUF32SEL,TF_FS(%rsp)
-	jne	1f
 	rdfsbase %rax
-1:	cmpw	$KUG32SEL,TF_GS(%rsp)
-	jne	2f
 	rdgsbase %rdx
 2:	swapgs
 	lfence
 	movq	PCPU(CURPCB),%rdi
 	testb	$CPUID_STDEXT_FSGSBASE,cpu_stdext_feature(%rip)
 	jz	4f
-	cmpw	$KUF32SEL,TF_FS(%rsp)
-	jne	3f
 	movq	%rax,PCB_FSBASE(%rdi)
-3:	cmpw	$KUG32SEL,TF_GS(%rsp)
-	jne	4f
 	movq	%rdx,PCB_GSBASE(%rdi)
 	orl	$PCB_FULL_IRET,PCB_FLAGS(%rdi)	/* full iret from user #gp */
 4:	call	handle_ibrs_entry
@@ -730,12 +722,8 @@ dbg_fromuserspace:
 	orl	$PCB_FULL_IRET,PCB_FLAGS(%rdi)
 	testb	$CPUID_STDEXT_FSGSBASE,cpu_stdext_feature(%rip)
 	jz	3f
-	cmpw	$KUF32SEL,TF_FS(%rsp)
-	jne	2f
 	rdfsbase %rax
 	movq	%rax,PCB_FSBASE(%rdi)
-2:	cmpw	$KUG32SEL,TF_GS(%rsp)
-	jne	3f
 	movl	$MSR_KGSBASE,%ecx
 	rdmsr
 	shlq	$32,%rdx
@@ -842,12 +830,8 @@ nmi_fromuserspace:
 	orl	$PCB_FULL_IRET,PCB_FLAGS(%rdi)
 	testb	$CPUID_STDEXT_FSGSBASE,cpu_stdext_feature(%rip)
 	jz	3f
-	cmpw	$KUF32SEL,TF_FS(%rsp)
-	jne	2f
 	rdfsbase %rax
 	movq	%rax,PCB_FSBASE(%rdi)
-2:	cmpw	$KUG32SEL,TF_GS(%rsp)
-	jne	3f
 	movl	$MSR_KGSBASE,%ecx
 	rdmsr
 	shlq	$32,%rdx
@@ -1177,15 +1161,12 @@ do_segs:
 	.globl	ld_fs
 ld_fs:
 	movw	%ax,%fs
-	cmpw	$KUF32SEL,%ax
-	jne	1f
 	movl	$MSR_FSBASE,%ecx
 	movl	PCB_FSBASE(%r8),%eax
 	movl	PCB_FSBASE+4(%r8),%edx
 	.globl	ld_fsbase
 ld_fsbase:
 	wrmsr
-1:
 	/* Restore %gs and gsbase */
 	movw	TF_GS(%rsp),%si
 	pushfq
@@ -1198,10 +1179,6 @@ ld_fsbase:
 	.globl	ld_gs
 ld_gs:
 	movw	%si,%gs
-	/* Save user %gs base into %r14d:%r15d */
-	rdmsr
-	movl	%eax,%r14d
-	movl	%edx,%r15d
 	/* Restore kernel %gs base */
 	movl	%r12d,%eax
 	movl	%r13d,%edx
@@ -1212,14 +1189,8 @@ ld_gs:
 	 * from the previously saved msr read.
 	 */
 	movl	$MSR_KGSBASE,%ecx
-	cmpw	$KUG32SEL,%si
-	jne	1f
 	movl	PCB_GSBASE(%r8),%eax
 	movl	PCB_GSBASE+4(%r8),%edx
-	jmp	ld_gsbase
-1:
-	movl	%r14d,%eax
-	movl	%r15d,%edx
 	.globl	ld_gsbase
 ld_gsbase:
 	wrmsr	/* May trap if non-canonical, but only for TLS. */
diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index ea0f164b2e56..e4109b0ff791 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -1786,10 +1786,8 @@ set_pcb_flags_fsgsbase(struct pcb *pcb, const u_int flags)
 	    (pcb->pcb_flags & PCB_FULL_IRET) == 0) {
 		r = intr_disable();
 		if ((pcb->pcb_flags & PCB_FULL_IRET) == 0) {
-			if (rfs() == _ufssel)
-				pcb->pcb_fsbase = rdfsbase();
-			if (rgs() == _ugssel)
-				pcb->pcb_gsbase = rdmsr(MSR_KGSBASE);
+			pcb->pcb_fsbase = rdfsbase();
+			pcb->pcb_gsbase = rdmsr(MSR_KGSBASE);
 		}
 		set_pcb_flags_raw(pcb, flags);
 		intr_restore(r);
diff --git a/sys/amd64/ia32/ia32_exception.S b/sys/amd64/ia32/ia32_exception.S
index 42d0ff6c638b..ef1a2c59a0af 100644
--- a/sys/amd64/ia32/ia32_exception.S
+++ b/sys/amd64/ia32/ia32_exception.S
@@ -54,10 +54,10 @@ int0x80_syscall_common:
 	movq	%rax,TF_RAX(%rsp)
 	movq	%rdx,TF_RDX(%rsp)
 	movq	%rcx,TF_RCX(%rsp)
+	movq	%r15,TF_R15(%rsp)
 	call	handle_ibrs_entry
 	sti
 	movq	%rsi,TF_RSI(%rsp)
-	movq	%r8,TF_R8(%rsp)
 	movq	%r9,TF_R9(%rsp)
 	movq	%rbx,TF_RBX(%rsp)
 	movq	%rbp,TF_RBP(%rsp)
@@ -66,7 +66,6 @@ int0x80_syscall_common:
 	movq	%r12,TF_R12(%rsp)
 	movq	%r13,TF_R13(%rsp)
 	movq	%r14,TF_R14(%rsp)
-	movq	%r15,TF_R15(%rsp)
 	movl	$TF_HASSEGS,TF_FLAGS(%rsp)
 	pushfq
 	andq	$~(PSL_D | PSL_AC),(%rsp)