[RFC v3 18/23] powerpc: Deliver SEGV signal on pkey violation

From: Ram Pai
Date: Wed Jun 21 2017 - 21:43:26 EST

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

This field can be used to reprogram the permission bits of
any valid pkey.

Similarly the value of the pkey, whose protection got violated,
is made available at 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 | 14 ++++++++++
arch/powerpc/kernel/signal_64.c | 14 ++++++++++
arch/powerpc/kernel/traps.c | 49 ++++++++++++++++++++++++++++++++++
arch/powerpc/mm/fault.c | 2 ++
8 files changed, 101 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..059766a 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;
}

@@ -661,6 +666,9 @@ static long restore_user_regs(struct pt_regs *regs,
long err;
unsigned int save_r2 = 0;
unsigned long msr;
+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+ unsigned long amr;
+#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
#ifdef CONFIG_VSX
int i;
#endif
@@ -750,6 +758,12 @@ static long restore_user_regs(struct pt_regs *regs,
return 1;
#endif /* CONFIG_SPE */

+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+ err |= __get_user(amr, &sr->mc_gregs[PT_AMR]);
+ if (!err && amr != get_paca()->paca_amr)
+ write_amr(amr);
+#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..35df2e4 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;
}

@@ -327,6 +331,9 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
unsigned long save_r13 = 0;
unsigned long msr;
struct pt_regs *regs = tsk->thread.regs;
+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+ unsigned long amr;
+#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
#ifdef CONFIG_VSX
int i;
#endif
@@ -406,6 +413,13 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
tsk->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = 0;
}
#endif
+
+#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
+ err |= __get_user(amr, &sc->gp_regs[PT_AMR]);
+ if (!err && amr != get_paca()->paca_amr)
+ write_amr(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