[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH] x86/PV: use 64-bit subtract to adjust guest RIP upon missing SYSCALL callbacks
When discussing the shrunk down version of the commit in question it was said (in reply to my conditional choosing of the width): "However, the 32bit case isn't actually interesting here. A guest can't execute a SYSCALL instruction on/across the 4G->0 boundary because the M2P is mapped NX up to the 4G boundary, so we can never reach this point with %eip < 2. Therefore, the 64bit-only form is the appropriate one to use, which solves any question of cleverness, or potential decode stalls it causes." Fixes: ca6fcf4321b3 ("x86/pv: Inject #UD for missing SYSCALL callbacks") Signed-off-by: Jan Beulich <JBeulich@xxxxxxxx> --- a/xen/arch/x86/x86_64/entry.S +++ b/xen/arch/x86/x86_64/entry.S @@ -42,7 +42,7 @@ ENTRY(switch_to_kernel) UNLIKELY_START(z, syscall_no_callback) /* TB_eip == 0 => #UD */ mov VCPU_trap_ctxt(%rbx), %rdi movl $X86_EXC_UD, UREGS_entry_vector(%rsp) - subl $2, UREGS_rip(%rsp) + subq $2, UREGS_rip(%rsp) mov X86_EXC_UD * TRAPINFO_sizeof + TRAPINFO_eip(%rdi), %rax testb $4, X86_EXC_UD * TRAPINFO_sizeof + TRAPINFO_flags(%rdi) setnz %cl
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