On Tue, 18 Sep 2018, Eric W. Biederman wrote: > There is only one code path that can generate a pkuerr signal. That > code path calls __bad_area_nosemaphore and can be dectected by testing > if si_code == SEGV_PKUERR. It can be seen from inspection that all of > the other tests in fill_sig_info_pkey are unnecessary. > > Therefore call force_sig_pkuerr directly from __bad_area_semaphore > and remove fill_sig_info_pkey. > > At the same time move the comment above force_sig_info_pkey into > bad_area_access_error, so that the documentation of about pkey
of about? Pick one please > generation races is not lost. > > Signed-off-by: "Eric W. Biederman" <[email protected]> > --- > arch/x86/mm/fault.c | 75 ++++++++++++++------------------------------- > 1 file changed, 23 insertions(+), 52 deletions(-) > > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c > index 11a93f14a674..ccfeed902eee 100644 > --- a/arch/x86/mm/fault.c > +++ b/arch/x86/mm/fault.c > @@ -153,56 +153,6 @@ is_prefetch(struct pt_regs *regs, unsigned long > error_code, unsigned long addr) > return prefetch; > } > > -/* > - * A protection key fault means that the PKRU value did not allow > - * access to some PTE. Userspace can figure out what PKRU was > - * from the XSAVE state, and this function fills out a field in > - * siginfo so userspace can discover which protection key was set > - * on the PTE. > - * > - * If we get here, we know that the hardware signaled a X86_PF_PK > - * fault and that there was a VMA once we got in the fault > - * handler. It does *not* guarantee that the VMA we find here > - * was the one that we faulted on. > - * > - * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4); > - * 2. T1 : set PKRU to deny access to pkey=4, touches page > - * 3. T1 : faults... > - * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5); > - * 5. T1 : enters fault handler, takes mmap_sem, etc... > - * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really > - * faulted on a pte with its pkey=4. > - */ > -static void fill_sig_info_pkey(int si_signo, int si_code, siginfo_t *info, > - u32 *pkey) > -{ > - /* This is effectively an #ifdef */ > - if (!boot_cpu_has(X86_FEATURE_OSPKE)) > - return; > - > - /* Fault not from Protection Keys: nothing to do */ > - if ((si_code != SEGV_PKUERR) || (si_signo != SIGSEGV)) > - return; > - /* > - * force_sig_info_fault() is called from a number of > - * contexts, some of which have a VMA and some of which > - * do not. The X86_PF_PK handing happens after we have a > - * valid VMA, so we should never reach this without a > - * valid VMA. > - */ > - if (!pkey) { > - WARN_ONCE(1, "PKU fault with no VMA passed in"); > - info->si_pkey = 0; > - return; > - } > - /* > - * si_pkey should be thought of as a strong hint, but not > - * absolutely guranteed to be 100% accurate because of > - * the race explained above. > - */ > - info->si_pkey = *pkey; > -} > - > static void > force_sig_info_fault(int si_signo, int si_code, unsigned long address, > struct task_struct *tsk, u32 *pkey) > @@ -215,8 +165,6 @@ force_sig_info_fault(int si_signo, int si_code, unsigned > long address, > info.si_code = si_code; > info.si_addr = (void __user *)address; > > - fill_sig_info_pkey(si_signo, si_code, &info, pkey); > - > force_sig_info(si_signo, &info, tsk); > } > > @@ -884,6 +832,9 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned > long error_code, > tsk->thread.error_code = error_code; > tsk->thread.trap_nr = X86_TRAP_PF; > > + if (si_code == SEGV_PKUERR) > + force_sig_pkuerr((void __user *)address, *pkey); > + > force_sig_info_fault(SIGSEGV, si_code, address, tsk, pkey); > > return; > @@ -949,6 +900,26 @@ bad_area_access_error(struct pt_regs *regs, unsigned > long error_code, > * if pkeys are compiled out. > */ > if (bad_area_access_from_pkeys(error_code, vma)) { > + /* > + * A protection key fault means that the PKRU value did not > allow > + * access to some PTE. Userspace can figure out what PKRU was > + * from the XSAVE state. This function captures the pkey from > + * the vma and passes it to userspace so userspace can discover > + * which protection key was set on the PTE. > + * > + * If we get here, we know that the hardware signaled a > X86_PF_PK > + * fault and that there was a VMA once we got in the fault > + * handler. It does *not* guarantee that the VMA we find here > + * was the one that we faulted on. > + * > + * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4); > + * 2. T1 : set PKRU to deny access to pkey=4, touches page > + * 3. T1 : faults... > + * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5); > + * 5. T1 : enters fault handler, takes mmap_sem, etc... > + * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really > + * faulted on a pte with its pkey=4. > + */ > u32 pkey = vma_pkey(vma); > __bad_area(regs, error_code, address, &pkey, SEGV_PKUERR); Newline between variable declaration and code please. With that fixed: Reviewed-by: Thomas Gleixner <[email protected]>
