[PATCH v37 19/24] x86/fault: Add helper function to sanitize error code

Jarkko Sakkinen
2020-09-11T12:49:42Z

From: Sean Christopherson <sean.j.christopherson@intel.com>

Add helper function to sanitize error code to prepare for vDSO exception
fixup, which will expose the error code to userspace and runs before
set_signal_archinfo(), i.e. suppresses the signal when fixup is successful.

Acked-by: Jethro Beekman <jethro@fortanix.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
---
arch/x86/mm/fault.c | 24 +++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 1a7cc6d3281a..9e5ec861aba0 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -555,6 +555,18 @@ pgtable_bad(struct pt_regs *regs, unsigned long error_code,
oops_end(flags, regs, sig);
}

+static void sanitize_error_code(unsigned long address,
+ unsigned long *error_code)
+{
+ /*
+ * To avoid leaking information about the kernel page
+ * table layout, pretend that user-mode accesses to
+ * kernel addresses are always protection faults.
+ */
+ if (address >= TASK_SIZE_MAX)
+ *error_code |= X86_PF_PROT;
+}
+
static void set_signal_archinfo(unsigned long address,
unsigned long error_code)
{
@@ -611,6 +623,8 @@ no_context(struct pt_regs *regs, unsigned long error_code,
* faulting through the emulate_vsyscall() logic.
*/
if (current->thread.sig_on_uaccess_err && signal) {
+ sanitize_error_code(address, &error_code);
+
set_signal_archinfo(address, error_code);

/* XXX: hwpoison faults will set the wrong code. */
@@ -759,13 +773,7 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
if (is_errata100(regs, address))
return;

- /*
- * To avoid leaking information about the kernel page table
- * layout, pretend that user-mode accesses to kernel addresses
- * are always protection faults.
- */
- if (address >= TASK_SIZE_MAX)
- error_code |= X86_PF_PROT;
+ sanitize_error_code(address, &error_code);

if (likely(show_unhandled_signals))
show_signal_msg(regs, error_code, address, tsk);
@@ -884,6 +892,8 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
if (is_prefetch(regs, error_code, address))
return;

+ sanitize_error_code(address, &error_code);
+
set_signal_archinfo(address, error_code);

#ifdef CONFIG_MEMORY_FAILURE
--
2.25.1