The branch stable/15 has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=b4bbe15fe4c7f168af996e1bea62b947f2fc500a
commit b4bbe15fe4c7f168af996e1bea62b947f2fc500a Author: Konstantin Belousov <[email protected]> AuthorDate: 2026-06-16 21:44:00 +0000 Commit: Konstantin Belousov <[email protected]> CommitDate: 2026-06-25 00:50:23 +0000 amd64: do not restore fsbase/gsbase for 32bit processes (cherry picked from commit c7e5802ab6e6230a5782a09c914585d055eb5223) --- sys/amd64/amd64/exception.S | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) diff --git a/sys/amd64/amd64/exception.S b/sys/amd64/amd64/exception.S index babfbacf92ef..afdcdeedf0f5 100644 --- a/sys/amd64/amd64/exception.S +++ b/sys/amd64/amd64/exception.S @@ -1161,12 +1161,15 @@ do_segs: .globl ld_fs ld_fs: movw %ax,%fs + testl $PCB_32BIT,PCB_FLAGS(%r8) + jnz after_ld_fsbase movl $MSR_FSBASE,%ecx movl PCB_FSBASE(%r8),%eax movl PCB_FSBASE+4(%r8),%edx .globl ld_fsbase ld_fsbase: wrmsr +after_ld_fsbase: /* Restore %gs and gsbase */ movw TF_GS(%rsp),%si pushfq @@ -1179,6 +1182,8 @@ ld_fsbase: .globl ld_gs ld_gs: movw %si,%gs + testl $PCB_32BIT,PCB_FLAGS(%r8) + jnz ld_gsbase_32 /* Restore kernel %gs base */ movl %r12d,%eax movl %r13d,%edx @@ -1194,6 +1199,8 @@ ld_gs: .globl ld_gsbase ld_gsbase: wrmsr /* May trap if non-canonical, but only for TLS. */ + +after_ld_gsbase: .globl ld_es ld_es: movw TF_ES(%rsp),%es @@ -1241,6 +1248,30 @@ ld_regs: doreti_iret: iretq + /* + * 32bit gsbase path. + * The KGSBASE is not loaded from the pcb_gsbase, instead we move + * the GSBASE value into KGSBASE right after loading user %gs, then + * restore kernel gsbase. + */ +ld_gsbase_32: + /* Read the user gsbase into %r14d:%r15d. */ + movl $MSR_GSBASE,%ecx + rdmsr + movl %eax,%r14d + movl %edx,%r15d + /* Restore kernel %gs base */ + movl %r12d,%eax + movl %r13d,%edx + wrmsr + popfq + /* Load the user gsbase into KGSBASE. */ + movl $MSR_KGSBASE,%ecx + movl %r14d,%eax + movl %r15d,%edx + wrmsr + jmp after_ld_gsbase + set_segs: movw $KUDSEL,%ax movw %ax,TF_DS(%rsp)
