[RFC v4 12/17] powerpc: Deliver SEGV signal on pkey violation

From: Ram Pai
Date: Tue Jun 27 2017 - 06:15:14 EST

The value of the AMR register at the time of exception
is made available in gp_regs[PT_AMR] of the siginfo.

The value of the pkey, whose protection got violated,
is made available in si_pkey field of the siginfo structure.

Signed-off-by: Ram Pai <linuxram@xxxxxxxxxx>
---
arch/powerpc/include/asm/paca.h | 1 +
arch/powerpc/include/uapi/asm/ptrace.h | 3 ++-
arch/powerpc/kernel/asm-offsets.c | 5 ++++
arch/powerpc/kernel/exceptions-64s.S | 16 +++++++++--
arch/powerpc/kernel/signal_32.c | 5 ++++
arch/powerpc/kernel/signal_64.c | 4 +++
arch/powerpc/kernel/traps.c | 49 ++++++++++++++++++++++++++++++++++
arch/powerpc/mm/fault.c | 2 ++
8 files changed, 82 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index 1c09f8f..a41afd3 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -92,6 +92,7 @@ struct paca_struct {
struct dtl_entry *dispatch_log_end;
#endif /* CONFIG_PPC_STD_MMU_64 */
u64 dscr_default; /* per-CPU default DSCR */
+ u64 paca_amr; /* value of amr at exception */

#ifdef CONFIG_PPC_STD_MMU_64
/*
diff --git a/arch/powerpc/include/uapi/asm/ptrace.h b/arch/powerpc/include/uapi/asm/ptrace.h
index 8036b38..7ec2428 100644
--- a/arch/powerpc/include/uapi/asm/ptrace.h
+++ b/arch/powerpc/include/uapi/asm/ptrace.h
@@ -108,8 +108,9 @@ struct pt_regs {
#define PT_DAR 41
#define PT_DSISR 42
#define PT_RESULT 43
-#define PT_DSCR 44
#define PT_REGS_COUNT 44
+#define PT_DSCR 44
+#define PT_AMR 45

#define PT_FPR0 48 /* each FP reg occupies 2 slots in this space */

diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 709e234..17f5d8a 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -241,6 +241,11 @@ int main(void)
OFFSET(PACAHWCPUID, paca_struct, hw_cpu_id);
OFFSET(PACAKEXECSTATE, paca_struct, kexec_state);
OFFSET(PACA_DSCR_DEFAULT, paca_struct, dscr_default);
+
+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+ OFFSET(PACA_AMR, paca_struct, paca_amr);
+#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
+
OFFSET(ACCOUNT_STARTTIME, paca_struct, accounting.starttime);
OFFSET(ACCOUNT_STARTTIME_USER, paca_struct, accounting.starttime_user);
OFFSET(ACCOUNT_USER_TIME, paca_struct, accounting.utime);
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 3fd0528..a4de1b4 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -493,9 +493,15 @@ EXC_COMMON_BEGIN(data_access_common)
ld r12,_MSR(r1)
ld r3,PACA_EXGEN+EX_DAR(r13)
lwz r4,PACA_EXGEN+EX_DSISR(r13)
- li r5,0x300
std r3,_DAR(r1)
std r4,_DSISR(r1)
+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+ andis. r0,r4,DSISR_KEYFAULT@h /* save AMR only if its a key fault */
+ beq+ 1f
+ mfspr r5,SPRN_AMR
+ std r5,PACA_AMR(r13)
+#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
+1: li r5,0x300
BEGIN_MMU_FTR_SECTION
b do_hash_page /* Try to handle as hpte fault */
MMU_FTR_SECTION_ELSE
@@ -561,9 +567,15 @@ EXC_COMMON_BEGIN(instruction_access_common)
ld r12,_MSR(r1)
ld r3,_NIP(r1)
andis. r4,r12,0x5820
- li r5,0x400
std r3,_DAR(r1)
std r4,_DSISR(r1)
+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+ andis. r0,r4,DSISR_KEYFAULT@h /* save AMR only if its a key fault */
+ beq+ 1f
+ mfspr r5,SPRN_AMR
+ std r5,PACA_AMR(r13)
+#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
+1: li r5,0x400
BEGIN_MMU_FTR_SECTION
b do_hash_page /* Try to handle as hpte fault */
MMU_FTR_SECTION_ELSE
diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 97bb138..9c4a7f3 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -500,6 +500,11 @@ static int save_user_regs(struct pt_regs *regs, struct mcontext __user *frame,
(unsigned long) &frame->tramp[2]);
}

+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+ if (__put_user(get_paca()->paca_amr, &frame->mc_gregs[PT_AMR]))
+ return 1;
+#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
+
return 0;
}

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index c83c115..86a4262 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -174,6 +174,10 @@ static long setup_sigcontext(struct sigcontext __user *sc,
if (set != NULL)
err |= __put_user(set->sig[0], &sc->oldmask);

+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+ err |= __put_user(get_paca()->paca_amr, &sc->gp_regs[PT_AMR]);
+#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
+
return err;
}

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index d4e545d..cc4bde8b 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -20,6 +20,7 @@
#include <linux/sched/debug.h>
#include <linux/kernel.h>
#include <linux/mm.h>
+#include <linux/pkeys.h>
#include <linux/stddef.h>
#include <linux/unistd.h>
#include <linux/ptrace.h>
@@ -247,6 +248,49 @@ void user_single_step_siginfo(struct task_struct *tsk,
info->si_addr = (void __user *)regs->nip;
}

+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+static void fill_sig_info_pkey(int si_code, siginfo_t *info, unsigned long addr)
+{
+ struct vm_area_struct *vma;
+
+ /* Fault not from Protection Keys: nothing to do */
+ if (si_code != SEGV_PKUERR)
+ return;
+
+ down_read(&current->mm->mmap_sem);
+ /*
+ * we could be racing with pkey_mprotect().
+ * If pkey_mprotect() wins the key value could
+ * get modified...xxx
+ */
+ vma = find_vma(current->mm, addr);
+ up_read(&current->mm->mmap_sem);
+
+ /*
+ * force_sig_info_fault() is called from a number of
+ * contexts, some of which have a VMA and some of which
+ * do not. The Pkey-fault handing happens after we have a
+ * valid VMA, so we should never reach this without a
+ * valid VMA.
+ */
+ if (!vma) {
+ WARN_ONCE(1, "Pkey fault with no VMA passed in");
+ info->si_pkey = 0;
+ return;
+ }
+
+ /*
+ * We could report the incorrect key because of the reason
+ * explained above.
+ *
+ * si_pkey should be thought off as a strong hint, but not
+ * an absolutely guarantee because of the race explained
+ * above.
+ */
+ info->si_pkey = vma_pkey(vma);
+}
+#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
+
void _exception(int signr, struct pt_regs *regs, int code, unsigned long addr)
{
siginfo_t info;
@@ -274,6 +318,11 @@ void _exception(int signr, struct pt_regs *regs, int code, unsigned long addr)
info.si_signo = signr;
info.si_code = code;
info.si_addr = (void __user *) addr;
+
+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+ fill_sig_info_pkey(code, &info, addr);
+#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
+
force_sig_info(signr, &info, current);
}

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 3d71984..0780a53 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -451,6 +451,8 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
is_exec, 0)) {
+ /* our caller may not have saved the amr. Lets save it */
+ get_paca()->paca_amr = read_amr();
code = SEGV_PKUERR;
goto bad_area;
}
--
1.8.3.1