[PATCH 10/10] sparc: fix livelock in uaccess

Al Viro
2023-01-31T20:07:26Z

sparc equivalent of 26178ec11ef3 "x86: mm: consolidate VM_FAULT_RETRY handling"
If e.g. get_user() triggers a page fault and a fatal signal is caught, we might
end up with handle_mm_fault() returning VM_FAULT_RETRY and not doing anything
to page tables. In such case we must *not* return to the faulting insn -
that would repeat the entire thing without making any progress; what we need
instead is to treat that as failed (user) memory access.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
arch/sparc/mm/fault_32.c | 5 ++++-
arch/sparc/mm/fault_64.c | 7 ++++++-
2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/sparc/mm/fault_32.c b/arch/sparc/mm/fault_32.c
index 91259f291c54..179295b14664 100644
--- a/arch/sparc/mm/fault_32.c
+++ b/arch/sparc/mm/fault_32.c
@@ -187,8 +187,11 @@ asmlinkage void do_sparc_fault(struct pt_regs *regs, int text_fault, int write,
*/
fault = handle_mm_fault(vma, address, flags, regs);

- if (fault_signal_pending(fault, regs))
+ if (fault_signal_pending(fault, regs)) {
+ if (!from_user)
+ goto no_context;
return;
+ }

/* The fault is fully completed (including releasing mmap lock) */
if (fault & VM_FAULT_COMPLETED)
diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c
index 4acc12eafbf5..d91305de694c 100644
--- a/arch/sparc/mm/fault_64.c
+++ b/arch/sparc/mm/fault_64.c
@@ -424,8 +424,13 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)

fault = handle_mm_fault(vma, address, flags, regs);

- if (fault_signal_pending(fault, regs))
+ if (fault_signal_pending(fault, regs)) {
+ if (regs->tstate & TSTATE_PRIV) {
+ insn = get_fault_insn(regs, insn);
+ goto handle_kernel_fault;
+ }
goto exit_exception;
+ }

/* The fault is fully completed (including releasing mmap lock) */
if (fault & VM_FAULT_COMPLETED)
--
2.30.2