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    SubjectRe: [PATCH 04/29] x86/livepatch: Validate __fentry__ location
    On Wed, 23 Feb 2022 15:05:42 +0100
    Peter Zijlstra <peterz@infradead.org> wrote:

    > On Wed, Feb 23, 2022 at 07:41:39AM -0500, Steven Rostedt wrote:
    > > On Wed, 23 Feb 2022 11:57:26 +0100
    > > Peter Zijlstra <peterz@infradead.org> wrote:
    > >
    > > > --- a/kernel/trace/ftrace.c
    > > > +++ b/kernel/trace/ftrace.c
    > > > @@ -1578,7 +1578,23 @@ unsigned long ftrace_location_range(unsi
    > > > */
    > > > unsigned long ftrace_location(unsigned long ip)
    > > > {
    > > > - return ftrace_location_range(ip, ip);
    > > > + struct dyn_ftrace *rec;
    > > > + unsigned long offset;
    > > > + unsigned long size;
    > > > +
    > > > + rec = lookup_rec(ip, ip);
    > > > + if (!rec) {
    > > > + if (!kallsyms_lookup_size_offset(ip, &size, &offset))
    > > > + goto out;
    > > > +
    > > > + rec = lookup_rec(ip - offset, (ip - offset) + size);
    > > > + }
    > > > +
    > >
    > > Please create a new function for this. Perhaps find_ftrace_location().
    > >
    > > ftrace_location() is used to see if the address given is a ftrace
    > > nop or not. This change will make it always return true.
    > >
    >
    > # git grep ftrace_location
    > arch/powerpc/include/asm/livepatch.h:#define klp_get_ftrace_location klp_get_ftrace_location
    > arch/powerpc/include/asm/livepatch.h:static inline unsigned long klp_get_ftrace_location(unsigned long faddr)
    > arch/powerpc/include/asm/livepatch.h: return ftrace_location_range(faddr, faddr + 16);
    > arch/powerpc/kernel/kprobes.c: faddr = ftrace_location_range((unsigned long)addr,
    > arch/x86/kernel/kprobes/core.c: faddr = ftrace_location(addr);
    > arch/x86/kernel/kprobes/core.c: * arch_check_ftrace_location(). Something went terribly wrong
    > include/linux/ftrace.h:unsigned long ftrace_location(unsigned long ip);
    > include/linux/ftrace.h:unsigned long ftrace_location_range(unsigned long start, unsigned long end);
    > include/linux/ftrace.h:static inline unsigned long ftrace_location(unsigned long ip)
    > kernel/bpf/trampoline.c:static int is_ftrace_location(void *ip)
    > kernel/bpf/trampoline.c: addr = ftrace_location((long)ip);
    > kernel/bpf/trampoline.c: ret = is_ftrace_location(ip);
    > kernel/kprobes.c: unsigned long faddr = ftrace_location((unsigned long)addr);
    > kernel/kprobes.c:static int check_ftrace_location(struct kprobe *p)
    > kernel/kprobes.c: ftrace_addr = ftrace_location((unsigned long)p->addr);
    > kernel/kprobes.c: ret = check_ftrace_location(p);
    > kernel/livepatch/patch.c:#ifndef klp_get_ftrace_location
    > kernel/livepatch/patch.c:static unsigned long klp_get_ftrace_location(unsigned long faddr)
    > kernel/livepatch/patch.c: return ftrace_location(faddr);
    > kernel/livepatch/patch.c: klp_get_ftrace_location((unsigned long)func->old_func);
    > kernel/livepatch/patch.c: klp_get_ftrace_location((unsigned long)func->old_func);
    > kernel/trace/ftrace.c: * ftrace_location_range - return the first address of a traced location
    > kernel/trace/ftrace.c:unsigned long ftrace_location_range(unsigned long start, unsigned long end)
    > kernel/trace/ftrace.c: * ftrace_location - return true if the ip giving is a traced location
    > kernel/trace/ftrace.c:unsigned long ftrace_location(unsigned long ip)
    > kernel/trace/ftrace.c: ret = ftrace_location_range((unsigned long)start,
    > kernel/trace/ftrace.c: if (!ftrace_location(ip))
    > kernel/trace/ftrace.c: ip = ftrace_location(ip);
    > kernel/trace/ftrace.c: ip = ftrace_location(ip);
    > kernel/trace/trace_kprobe.c: * Since ftrace_location_range() does inclusive range check, we need
    > kernel/trace/trace_kprobe.c: return !ftrace_location_range(addr, addr + size - 1);
    >
    > and yet almost every caller takes the address it returns...

    And they check if the returned value is 0 or not. If it is zero, it lets
    them know it isn't an ftrace location.

    -- Steve

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