From: Björn Töpel bjorn@rivosinc.com
commit 416721ff05fddc58ca531b6f069de250301de6e5 upstream.
Commit 21855cac82d3 ("riscv/mm: Prevent kernel module to access user memory without uaccess routines") added early exits/deaths for page faults stemming from accesses to user-space without using proper uaccess routines (where sstatus.SUM is set).
Unfortunatly, this is too strict for some BPF programs, which relies on BPF exhandler fixups. These BPF programs loads "BTF pointers". A BTF pointers could either be a valid kernel pointer or NULL, but not a userspace address.
Resolve the problem by calling the fixup handler in the early exit path.
Fixes: 21855cac82d3 ("riscv/mm: Prevent kernel module to access user memory without uaccess routines") Signed-off-by: Björn Töpel bjorn@rivosinc.com Link: https://lore.kernel.org/r/20230214162515.184827-1-bjorn@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/riscv/mm/fault.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
--- a/arch/riscv/mm/fault.c +++ b/arch/riscv/mm/fault.c @@ -271,10 +271,12 @@ asmlinkage void do_page_fault(struct pt_ if (user_mode(regs)) flags |= FAULT_FLAG_USER;
- if (!user_mode(regs) && addr < TASK_SIZE && - unlikely(!(regs->status & SR_SUM))) - die_kernel_fault("access to user memory without uaccess routines", - addr, regs); + if (!user_mode(regs) && addr < TASK_SIZE && unlikely(!(regs->status & SR_SUM))) { + if (fixup_exception(regs)) + return; + + die_kernel_fault("access to user memory without uaccess routines", addr, regs); + }
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);