If a memory fault occurs that is due to an overlay/pkey fault, report that to userspace with a SEGV_PKUERR.
Signed-off-by: Joey Gouly joey.gouly@arm.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Will Deacon will@kernel.org Reviewed-by: Catalin Marinas catalin.marinas@arm.com --- arch/arm64/include/asm/traps.h | 1 + arch/arm64/kernel/traps.c | 6 ++++ arch/arm64/mm/fault.c | 55 +++++++++++++++++++++++++++++++++- 3 files changed, 61 insertions(+), 1 deletion(-)
diff --git arch/arm64/include/asm/traps.h arch/arm64/include/asm/traps.h index eefe766d6161..d780d1bd2eac 100644 --- arch/arm64/include/asm/traps.h +++ arch/arm64/include/asm/traps.h @@ -25,6 +25,7 @@ try_emulate_armv8_deprecated(struct pt_regs *regs, u32 insn) void force_signal_inject(int signal, int code, unsigned long address, unsigned long err); void arm64_notify_segfault(unsigned long addr); void arm64_force_sig_fault(int signo, int code, unsigned long far, const char *str); +void arm64_force_sig_fault_pkey(unsigned long far, const char *str, int pkey); void arm64_force_sig_mceerr(int code, unsigned long far, short lsb, const char *str); void arm64_force_sig_ptrace_errno_trap(int errno, unsigned long far, const char *str);
diff --git arch/arm64/kernel/traps.c arch/arm64/kernel/traps.c index 9e22683aa921..9a11bb0db284 100644 --- arch/arm64/kernel/traps.c +++ arch/arm64/kernel/traps.c @@ -273,6 +273,12 @@ void arm64_force_sig_fault(int signo, int code, unsigned long far, force_sig_fault(signo, code, (void __user *)far); }
+void arm64_force_sig_fault_pkey(unsigned long far, const char *str, int pkey) +{ + arm64_show_signal(SIGSEGV, str); + force_sig_pkuerr((void __user *)far, pkey); +} + void arm64_force_sig_mceerr(int code, unsigned long far, short lsb, const char *str) { diff --git arch/arm64/mm/fault.c arch/arm64/mm/fault.c index 451ba7cbd5ad..a68055150950 100644 --- arch/arm64/mm/fault.c +++ arch/arm64/mm/fault.c @@ -23,6 +23,7 @@ #include <linux/sched/debug.h> #include <linux/highmem.h> #include <linux/perf_event.h> +#include <linux/pkeys.h> #include <linux/preempt.h> #include <linux/hugetlb.h>
@@ -486,6 +487,23 @@ static void do_bad_area(unsigned long far, unsigned long esr, } }
+static bool fault_from_pkey(unsigned long esr, struct vm_area_struct *vma, + unsigned int mm_flags) +{ + unsigned long iss2 = ESR_ELx_ISS2(esr); + + if (!system_supports_poe()) + return false; + + if (iss2 & ESR_ELx_Overlay) + return true; + + return !arch_vma_access_permitted(vma, + mm_flags & FAULT_FLAG_WRITE, + mm_flags & FAULT_FLAG_INSTRUCTION, + false); +} + static bool is_el0_instruction_abort(unsigned long esr) { return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_LOW; @@ -511,6 +529,7 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr, unsigned long addr = untagged_addr(far); struct vm_area_struct *vma; int si_code; + int pkey = -1;
if (kprobe_page_fault(regs, esr)) return 0; @@ -575,6 +594,16 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr, count_vm_vma_lock_event(VMA_LOCK_SUCCESS); goto bad_area; } + + if (fault_from_pkey(esr, vma, mm_flags)) { + pkey = vma_pkey(vma); + vma_end_read(vma); + fault = 0; + si_code = SEGV_PKUERR; + count_vm_vma_lock_event(VMA_LOCK_SUCCESS); + goto bad_area; + } + fault = handle_mm_fault(vma, addr, mm_flags | FAULT_FLAG_VMA_LOCK, regs); if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED))) vma_end_read(vma); @@ -610,7 +639,16 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr, goto bad_area; }
+ if (fault_from_pkey(esr, vma, mm_flags)) { + pkey = vma_pkey(vma); + mmap_read_unlock(mm); + fault = 0; + si_code = SEGV_PKUERR; + goto bad_area; + } + fault = handle_mm_fault(vma, addr, mm_flags, regs); + /* Quick path to respond to signals */ if (fault_signal_pending(fault, regs)) { if (!user_mode(regs)) @@ -669,8 +707,23 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
arm64_force_sig_mceerr(BUS_MCEERR_AR, far, lsb, inf->name); } else { + /* + * The pkey value that we return to userspace can be different + * from the pkey that caused the fault. + * + * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4); + * 2. T1 : set POR_EL0 to deny access to pkey=4, touches, page + * 3. T1 : faults... + * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5); + * 5. T1 : enters fault handler, takes mmap_lock, etc... + * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really + * faulted on a pte with its pkey=4. + */ /* Something tried to access memory that out of memory map */ - arm64_force_sig_fault(SIGSEGV, si_code, far, inf->name); + if (si_code == SEGV_PKUERR) + arm64_force_sig_fault_pkey(far, inf->name, pkey); + else + arm64_force_sig_fault(SIGSEGV, si_code, far, inf->name); }
return 0;