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Subject[PATCH v2 10/14] x86/fault: Bypass no_context() for implicit kernel faults from usermode
Date
We can drop an indentation level and remove the last
user_mode(regs) == true caller of no_context() by directly OOPSing for
implicit kernel faults from usermode.

Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/mm/fault.c | 59 ++++++++++++++++++++++++---------------------
1 file changed, 32 insertions(+), 27 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 8b8bd0a4f4b2..f735639455a5 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -825,44 +825,49 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
{
struct task_struct *tsk = current;

- /* User mode accesses just cause a SIGSEGV */
- if (user_mode(regs) && (error_code & X86_PF_USER)) {
- /*
- * It's possible to have interrupts off here:
- */
- local_irq_enable();
+ if (!user_mode(regs)) {
+ no_context(regs, error_code, address, pkey, si_code);
+ return;
+ }

- /*
- * Valid to do another page fault here because this one came
- * from user space:
- */
- if (is_prefetch(regs, error_code, address))
- return;
+ if (!(error_code & X86_PF_USER)) {
+ /* Implicit user access to kernel memory -- just oops */
+ page_fault_oops(regs, error_code, address);
+ return;
+ }

- if (is_errata100(regs, address))
- return;
+ /*
+ * User mode accesses just cause a SIGSEGV.
+ * It's possible to have interrupts off here:
+ */
+ local_irq_enable();

- sanitize_error_code(address, &error_code);
+ /*
+ * Valid to do another page fault here because this one came
+ * from user space:
+ */
+ if (is_prefetch(regs, error_code, address))
+ return;

- if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
- return;
+ if (is_errata100(regs, address))
+ return;

- if (likely(show_unhandled_signals))
- show_signal_msg(regs, error_code, address, tsk);
+ sanitize_error_code(address, &error_code);

- set_signal_archinfo(address, error_code);
+ if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
+ return;

- if (si_code == SEGV_PKUERR)
- force_sig_pkuerr((void __user *)address, pkey);
+ if (likely(show_unhandled_signals))
+ show_signal_msg(regs, error_code, address, tsk);

- force_sig_fault(SIGSEGV, si_code, (void __user *)address);
+ set_signal_archinfo(address, error_code);

- local_irq_disable();
+ if (si_code == SEGV_PKUERR)
+ force_sig_pkuerr((void __user *)address, pkey);

- return;
- }
+ force_sig_fault(SIGSEGV, si_code, (void __user *)address);

- no_context(regs, error_code, address, SIGSEGV, si_code);
+ local_irq_disable();
}

static noinline void
--
2.29.2
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