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Subject[tip: x86/mm] x86/fault: Bypass no_context() for implicit kernel faults from usermode
The following commit has been merged into the x86/mm branch of tip:

Commit-ID: 5042d40a264c8a508d58ed71e4c07b05175b3635
Gitweb: https://git.kernel.org/tip/5042d40a264c8a508d58ed71e4c07b05175b3635
Author: Andy Lutomirski <luto@kernel.org>
AuthorDate: Tue, 09 Feb 2021 18:33:42 -08:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Wed, 10 Feb 2021 14:39:52 +01:00

x86/fault: Bypass no_context() for implicit kernel faults from usermode

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.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/6e3d1129494a8de1e59d28012286e3a292a2296e.1612924255.git.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 dbf6a94..187975b 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -826,44 +826,49 @@ __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
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