kprobes: Remove kprobe::fault_handler

The reason for kprobe::fault_handler(), as given by their comment:

 * We come here because instructions in the pre/post
 * handler caused the page_fault, this could happen
 * if handler tries to access user space by
 * copy_from_user(), get_user() etc. Let the
 * user-specified handler try to fix it first.

Is just plain bad. Those other handlers are ran from non-preemptible
context and had better use _nofault() functions. Also, there is no
upstream usage of this.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20210525073213.561116662@infradead.org

diff --git a/Documentation/trace/kprobes.rst b/Documentation/trace/kprobes.rst
index b757b6d..998149c 100644 (file)
--- a/Documentation/trace/kprobes.rst
+++ b/Documentation/trace/kprobes.rst
@@ -362,14 +362,11 @@ register_kprobe
        #include <linux/kprobes.h>
        int register_kprobe(struct kprobe *kp);
 
-Sets a breakpoint at the address kp->addr.  When the breakpoint is
-hit, Kprobes calls kp->pre_handler.  After the probed instruction
-is single-stepped, Kprobe calls kp->post_handler.  If a fault
-occurs during execution of kp->pre_handler or kp->post_handler,
-or during single-stepping of the probed instruction, Kprobes calls
-kp->fault_handler.  Any or all handlers can be NULL. If kp->flags
-is set KPROBE_FLAG_DISABLED, that kp will be registered but disabled,
-so, its handlers aren't hit until calling enable_kprobe(kp).
+Sets a breakpoint at the address kp->addr.  When the breakpoint is hit, Kprobes
+calls kp->pre_handler.  After the probed instruction is single-stepped, Kprobe
+calls kp->post_handler.  Any or all handlers can be NULL. If kp->flags is set
+KPROBE_FLAG_DISABLED, that kp will be registered but disabled, so, its handlers
+aren't hit until calling enable_kprobe(kp).
 
 .. note::
 
@@ -415,17 +412,6 @@ User's post-handler (kp->post_handler)::
 p and regs are as described for the pre_handler.  flags always seems
 to be zero.
 
-User's fault-handler (kp->fault_handler)::
-
-       #include <linux/kprobes.h>
-       #include <linux/ptrace.h>
-       int fault_handler(struct kprobe *p, struct pt_regs *regs, int trapnr);
-
-p and regs are as described for the pre_handler.  trapnr is the
-architecture-specific trap number associated with the fault (e.g.,
-on i386, 13 for a general protection fault or 14 for a page fault).
-Returns 1 if it successfully handled the exception.
-
 register_kretprobe
 ------------------
 

diff --git a/arch/arc/kernel/kprobes.c b/arch/arc/kernel/kprobes.c
index cabef45..9f5b39f 100644 (file)
--- a/arch/arc/kernel/kprobes.c
+++ b/arch/arc/kernel/kprobes.c
@@ -323,16 +323,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned long trapnr)
                 */
                kprobes_inc_nmissed_count(cur);
 
-               /*
-                * We come here because instructions in the pre/post
-                * handler caused the page_fault, this could happen
-                * if handler tries to access user space by
-                * copy_from_user(), get_user() etc. Let the
-                * user-specified handler try to fix it first.
-                */
-               if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
-                       return 1;
-
                /*
                 * In case the user-specified fault handler returned zero,
                 * try to fix up.

diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
index a965311..7b9b9a5 100644 (file)
--- a/arch/arm/probes/kprobes/core.c
+++ b/arch/arm/probes/kprobes/core.c
@@ -358,15 +358,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
                 */
                kprobes_inc_nmissed_count(cur);
 
-               /*
-                * We come here because instructions in the pre/post
-                * handler caused the page_fault, this could happen
-                * if handler tries to access user space by
-                * copy_from_user(), get_user() etc. Let the
-                * user-specified handler try to fix it.
-                */
-               if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
-                       return 1;
                break;
 
        default:

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index d607c99..f6b088e 100644 (file)
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -283,16 +283,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
                 */
                kprobes_inc_nmissed_count(cur);
 
-               /*
-                * We come here because instructions in the pre/post
-                * handler caused the page_fault, this could happen
-                * if handler tries to access user space by
-                * copy_from_user(), get_user() etc. Let the
-                * user-specified handler try to fix it first.
-                */
-               if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
-                       return 1;
-
                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.

diff --git a/arch/csky/kernel/probes/kprobes.c b/arch/csky/kernel/probes/kprobes.c
index 589f090..e0e973e 100644 (file)
--- a/arch/csky/kernel/probes/kprobes.c
+++ b/arch/csky/kernel/probes/kprobes.c
@@ -301,16 +301,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int trapnr)
                 */
                kprobes_inc_nmissed_count(cur);
 
-               /*
-                * We come here because instructions in the pre/post
-                * handler caused the page_fault, this could happen
-                * if handler tries to access user space by
-                * copy_from_user(), get_user() etc. Let the
-                * user-specified handler try to fix it first.
-                */
-               if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
-                       return 1;
-
                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.

diff --git a/arch/ia64/kernel/kprobes.c b/arch/ia64/kernel/kprobes.c
index fc1ff8a..6efed4e 100644 (file)
--- a/arch/ia64/kernel/kprobes.c
+++ b/arch/ia64/kernel/kprobes.c
@@ -850,15 +850,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
                 */
                kprobes_inc_nmissed_count(cur);
 
-               /*
-                * We come here because instructions in the pre/post
-                * handler caused the page_fault, this could happen
-                * if handler tries to access user space by
-                * copy_from_user(), get_user() etc. Let the
-                * user-specified handler try to fix it first.
-                */
-               if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
-                       return 1;
                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.

diff --git a/arch/mips/kernel/kprobes.c b/arch/mips/kernel/kprobes.c
index 54dfba8..75bff0f 100644 (file)
--- a/arch/mips/kernel/kprobes.c
+++ b/arch/mips/kernel/kprobes.c
@@ -403,9 +403,6 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 
-       if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
-               return 1;
-
        if (kcb->kprobe_status & KPROBE_HIT_SS) {
                resume_execution(cur, regs, kcb);
                regs->cp0_status |= kcb->kprobe_old_SR;

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 01ab216..75b4e87 100644 (file)
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -508,16 +508,6 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
                 */
                kprobes_inc_nmissed_count(cur);
 
-               /*
-                * We come here because instructions in the pre/post
-                * handler caused the page_fault, this could happen
-                * if handler tries to access user space by
-                * copy_from_user(), get_user() etc. Let the
-                * user-specified handler try to fix it first.
-                */
-               if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
-                       return 1;
-
                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.

diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
index 10b965c..923b5ea 100644 (file)
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -283,16 +283,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int trapnr)
                 */
                kprobes_inc_nmissed_count(cur);
 
-               /*
-                * We come here because instructions in the pre/post
-                * handler caused the page_fault, this could happen
-                * if handler tries to access user space by
-                * copy_from_user(), get_user() etc. Let the
-                * user-specified handler try to fix it first.
-                */
-               if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
-                       return 1;
-
                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.

diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index aae24dc..ad631e3 100644 (file)
--- a/arch/s390/kernel/kprobes.c
+++ b/arch/s390/kernel/kprobes.c
@@ -452,16 +452,6 @@ static int kprobe_trap_handler(struct pt_regs *regs, int trapnr)
                 */
                kprobes_inc_nmissed_count(p);
 
-               /*
-                * We come here because instructions in the pre/post
-                * handler caused the page_fault, this could happen
-                * if handler tries to access user space by
-                * copy_from_user(), get_user() etc. Let the
-                * user-specified handler try to fix it first.
-                */
-               if (p->fault_handler && p->fault_handler(p, regs, trapnr))
-                       return 1;
-
                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.

diff --git a/arch/sh/kernel/kprobes.c b/arch/sh/kernel/kprobes.c
index 756100b..5826342 100644 (file)
--- a/arch/sh/kernel/kprobes.c
+++ b/arch/sh/kernel/kprobes.c
@@ -389,16 +389,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
                 */
                kprobes_inc_nmissed_count(cur);
 
-               /*
-                * We come here because instructions in the pre/post
-                * handler caused the page_fault, this could happen
-                * if handler tries to access user space by
-                * copy_from_user(), get_user() etc. Let the
-                * user-specified handler try to fix it first.
-                */
-               if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
-                       return 1;
-
                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.

diff --git a/arch/sparc/kernel/kprobes.c b/arch/sparc/kernel/kprobes.c
index 217c21a..db4e341 100644 (file)
--- a/arch/sparc/kernel/kprobes.c
+++ b/arch/sparc/kernel/kprobes.c
@@ -352,16 +352,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
                 */
                kprobes_inc_nmissed_count(cur);
 
-               /*
-                * We come here because instructions in the pre/post
-                * handler caused the page_fault, this could happen
-                * if handler tries to access user space by
-                * copy_from_user(), get_user() etc. Let the
-                * user-specified handler try to fix it first.
-                */
-               if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
-                       return 1;
-
                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index d3d6554..cfcdf4b 100644 (file)
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1110,16 +1110,6 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
                 * these specific fault cases.
                 */
                kprobes_inc_nmissed_count(cur);
-
-               /*
-                * We come here because instructions in the pre/post
-                * handler caused the page_fault, this could happen
-                * if handler tries to access user space by
-                * copy_from_user(), get_user() etc. Let the
-                * user-specified handler try to fix it first.
-                */
-               if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
-                       return 1;
        }
 
        return 0;

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 1883a4a..523ffc7 100644 (file)
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -54,8 +54,6 @@ struct kretprobe_instance;
 typedef int (*kprobe_pre_handler_t) (struct kprobe *, struct pt_regs *);
 typedef void (*kprobe_post_handler_t) (struct kprobe *, struct pt_regs *,
                                       unsigned long flags);
-typedef int (*kprobe_fault_handler_t) (struct kprobe *, struct pt_regs *,
-                                      int trapnr);
 typedef int (*kretprobe_handler_t) (struct kretprobe_instance *,
                                    struct pt_regs *);
 
@@ -83,12 +81,6 @@ struct kprobe {
        /* Called after addr is executed, unless... */
        kprobe_post_handler_t post_handler;
 
-       /*
-        * ... called if executing addr causes a fault (eg. page fault).
-        * Return 1 if it handled fault, otherwise kernel will see it.
-        */
-       kprobe_fault_handler_t fault_handler;
-
        /* Saved opcode (which has been replaced with breakpoint) */
        kprobe_opcode_t opcode;
 

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 745f08f..e41385a 100644 (file)
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1183,23 +1183,6 @@ static void aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
 }
 NOKPROBE_SYMBOL(aggr_post_handler);
 
-static int aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
-                             int trapnr)
-{
-       struct kprobe *cur = __this_cpu_read(kprobe_instance);
-
-       /*
-        * if we faulted "during" the execution of a user specified
-        * probe handler, invoke just that probe's fault handler
-        */
-       if (cur && cur->fault_handler) {
-               if (cur->fault_handler(cur, regs, trapnr))
-                       return 1;
-       }
-       return 0;
-}
-NOKPROBE_SYMBOL(aggr_fault_handler);
-
 /* Walks the list and increments nmissed count for multiprobe case */
 void kprobes_inc_nmissed_count(struct kprobe *p)
 {
@@ -1330,7 +1313,6 @@ static void init_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
        ap->addr = p->addr;
        ap->flags = p->flags & ~KPROBE_FLAG_OPTIMIZED;
        ap->pre_handler = aggr_pre_handler;
-       ap->fault_handler = aggr_fault_handler;
        /* We don't care the kprobe which has gone. */
        if (p->post_handler && !kprobe_gone(p))
                ap->post_handler = aggr_post_handler;
@@ -2014,7 +1996,6 @@ int register_kretprobe(struct kretprobe *rp)
 
        rp->kp.pre_handler = pre_handler_kretprobe;
        rp->kp.post_handler = NULL;
-       rp->kp.fault_handler = NULL;
 
        /* Pre-allocate memory for max kretprobe instances */
        if (rp->maxactive <= 0) {

diff --git a/samples/kprobes/kprobe_example.c b/samples/kprobes/kprobe_example.c
index c495664..4b2f318 100644 (file)
--- a/samples/kprobes/kprobe_example.c
+++ b/samples/kprobes/kprobe_example.c
@@ -94,26 +94,11 @@ static void __kprobes handler_post(struct kprobe *p, struct pt_regs *regs,
 #endif
 }
 
-/*
- * fault_handler: this is called if an exception is generated for any
- * instruction within the pre- or post-handler, or when Kprobes
- * single-steps the probed instruction.
- */
-static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
-{
-       pr_info("fault_handler: p->addr = 0x%p, trap #%dn", p->addr, trapnr);
-       /* Return 0 because we don't handle the fault. */
-       return 0;
-}
-/* NOKPROBE_SYMBOL() is also available */
-NOKPROBE_SYMBOL(handler_fault);
-
 static int __init kprobe_init(void)
 {
        int ret;
        kp.pre_handler = handler_pre;
        kp.post_handler = handler_post;
-       kp.fault_handler = handler_fault;
 
        ret = register_kprobe(&kp);
        if (ret < 0) {