[RFC v3 08/19] arch: um: add shim to trap to allow installing a fault catcher for tests

[Brendan Higgins]

Add context to current thread that allows a test to specify that it
wants to skip the normal checks to run an installed fault catcher.

Signed-off-by: Brendan Higgins <brendanhigg...@google.com>
---
 arch/um/include/asm/processor-generic.h |  4 +++-
 arch/um/kernel/trap.c                   | 15 +++++++++++----
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/arch/um/include/asm/processor-generic.h 
b/arch/um/include/asm/processor-generic.h
index b58b746d3f2ca..d566cd416ff02 100644
--- a/arch/um/include/asm/processor-generic.h
+++ b/arch/um/include/asm/processor-generic.h
@@ -27,6 +27,7 @@ struct thread_struct {
        struct task_struct *prev_sched;
        struct arch_thread arch;
        jmp_buf switch_buf;
+       bool is_running_test;
        struct {
                int op;
                union {
@@ -51,7 +52,8 @@ struct thread_struct {
        .fault_addr             = NULL, \
        .prev_sched             = NULL, \
        .arch                   = INIT_ARCH_THREAD, \
-       .request                = { 0 } \
+       .request                = { 0 }, \
+       .is_running_test        = false, \
 }
 
 static inline void release_thread(struct task_struct *task)
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index cced829460427..bf90e678b3d71 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -201,6 +201,12 @@ void segv_handler(int sig, struct siginfo *unused_si, 
struct uml_pt_regs *regs)
        segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
 }
 
+static void segv_run_catcher(jmp_buf *catcher, void *fault_addr)
+{
+       current->thread.fault_addr = fault_addr;
+       UML_LONGJMP(catcher, 1);
+}
+
 /*
  * We give a *copy* of the faultinfo in the regs to segv.
  * This must be done, since nesting SEGVs could overwrite
@@ -219,7 +225,10 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, 
int is_user,
        if (!is_user && regs)
                current->thread.segv_regs = container_of(regs, struct pt_regs, 
regs);
 
-       if (!is_user && (address >= start_vm) && (address < end_vm)) {
+       catcher = current->thread.fault_catcher;
+       if (catcher && current->thread.is_running_test)
+               segv_run_catcher(catcher, (void *) address);
+       else if (!is_user && (address >= start_vm) && (address < end_vm)) {
                flush_tlb_kernel_vm();
                goto out;
        }
@@ -246,12 +255,10 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, 
int is_user,
                address = 0;
        }
 
-       catcher = current->thread.fault_catcher;
        if (!err)
                goto out;
        else if (catcher != NULL) {
-               current->thread.fault_addr = (void *) address;
-               UML_LONGJMP(catcher, 1);
+               segv_run_catcher(catcher, (void *) address);
        }
        else if (current->thread.fault_addr != NULL)
                panic("fault_addr set but no fault catcher");
-- 
2.20.0.rc0.387.gc7a69e6b6c-goog

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