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@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
---
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;
--
2.25.1
