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
generation races is not lost.
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
---
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);
}
--
2.17.1
