Applied, thanks! Luca Dariz, le jeu. 15 juin 2023 23:49:31 +0200, a ecrit: > When entering a syscall we're still using the user stack, so we can't > reliably handle exceptions or interrupts, otherwise a user thread can > easily crash the machine with an invalid stack. Instead, disable > interrupts and (hopefullly) avoid traps in the fragments where we need > to have the user stack in RSP. > > * i386/i386/ldt.c: mask interrupts and IOPL on syscall entry > * x86_64/locore.S: keep interrupts disabled when we use the user stack > --- > i386/i386/ldt.c | 3 ++- > x86_64/locore.S | 4 +++- > 2 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/i386/i386/ldt.c b/i386/i386/ldt.c > index 4d7ec19a..5db36426 100644 > --- a/i386/i386/ldt.c > +++ b/i386/i386/ldt.c > @@ -27,6 +27,7 @@ > * "Local" descriptor table. At the moment, all tasks use the > * same LDT. > */ > +#include <mach/machine/eflags.h> > #include <mach/machine/vm_types.h> > #include <mach/xen.h> > > @@ -75,7 +76,7 @@ ldt_fill(struct real_descriptor *myldt, struct > real_descriptor *mygdt) > wrmsr(MSR_REG_EFER, rdmsr(MSR_REG_EFER) | MSR_EFER_SCE); > wrmsr(MSR_REG_LSTAR, (vm_offset_t)syscall64); > wrmsr(MSR_REG_STAR, ((((long)USER_CS - 16) << 16) | (long)KERNEL_CS) > << 32); > - wrmsr(MSR_REG_FMASK, 0); // ? > + wrmsr(MSR_REG_FMASK, EFL_IF | EFL_IOPL_USER); > #else /* defined(__x86_64__) && ! defined(USER32) */ > fill_ldt_gate(myldt, USER_SCALL, > (vm_offset_t)&syscall, KERNEL_CS, > diff --git a/x86_64/locore.S b/x86_64/locore.S > index a6697fb9..16b0dde5 100644 > --- a/x86_64/locore.S > +++ b/x86_64/locore.S > @@ -1405,9 +1405,10 @@ ENTRY(syscall64) > mov %r11,%rbx /* prepare for error handling */ > mov %r10,%rcx /* fix arg3 location according to C ABI > */ > > - /* switch to kernel stack */ > + /* switch to kernel stack, then we can enable interrupts */ > CPU_NUMBER(%r11) > movq CX(EXT(kernel_stack),%r11),%rsp > + sti > > /* Now we have saved state and args 1-6 are in place. > * Before invoking the syscall we do some bound checking and, > @@ -1468,6 +1469,7 @@ _syscall64_check_for_ast: > > _syscall64_restore_state: > /* Restore thread state and return to user using sysret. */ > + cli /* block interrupts when using the user stack in kernel space */ > movq CX(EXT(active_threads),%r11),%r11 /* point to current thread */ > movq TH_PCB(%r11),%r11 /* point to pcb */ > addq $ PCB_ISS,%r11 /* point to saved state */ > -- > 2.39.2 > >
-- Samuel --- Pour une évaluation indépendante, transparente et rigoureuse ! Je soutiens la Commission d'Évaluation de l'Inria.
