From: Jan Beulich Date: Tue, 2 Jul 2024 10:01:21 +0000 (+0200) Subject: x86/entry: don't clear DF when raising #UD for lack of syscall handler X-Git-Tag: 4.19.0-rc2~16 X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=d2fe9ab3048d503869ec81bc49db07e55a4a2386;p=xen.git x86/entry: don't clear DF when raising #UD for lack of syscall handler While doing so is intentional when invoking the actual callback, to mimic a hard-coded SYCALL_MASK / FMASK MSR, the same should not be done when no handler is available and hence #UD is raised. Fixes: ca6fcf4321b3 ("x86/pv: Inject #UD for missing SYSCALL callbacks") Reported-by: Andrew Cooper Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper Release-Acked-By: Oleksii Kurochko --- diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S index df015589ce..b8482de8ee 100644 --- a/xen/arch/x86/x86_64/entry.S +++ b/xen/arch/x86/x86_64/entry.S @@ -38,6 +38,14 @@ FUNC_LOCAL(switch_to_kernel) setc %cl leal (,%rcx,TBF_INTERRUPT),%ecx + /* + * The PV ABI hardcodes the (guest-inaccessible and virtual) + * SYSCALL_MASK MSR such that DF (and nothing else) would be cleared. + * Note that the equivalent of IF (VGCF_syscall_disables_events) is + * dealt with separately above. + */ + mov $~X86_EFLAGS_DF, %esi + test %rax, %rax UNLIKELY_START(z, syscall_no_callback) /* TB_eip == 0 => #UD */ mov VCPU_trap_ctxt(%rbx), %rdi @@ -47,12 +55,14 @@ UNLIKELY_START(z, syscall_no_callback) /* TB_eip == 0 => #UD */ testb $4, X86_EXC_UD * TRAPINFO_sizeof + TRAPINFO_flags(%rdi) setnz %cl lea TBF_EXCEPTION(, %rcx, TBF_INTERRUPT), %ecx + or $~0, %esi /* Don't clear DF */ UNLIKELY_END(syscall_no_callback) movq %rax,TRAPBOUNCE_eip(%rdx) movb %cl,TRAPBOUNCE_flags(%rdx) call create_bounce_frame - andl $~X86_EFLAGS_DF,UREGS_eflags(%rsp) + /* Conditionally clear DF */ + and %esi, UREGS_eflags(%rsp) /* %rbx: struct vcpu */ test_all_events: ASSERT_NOT_IN_ATOMIC