* Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> wrote (on 2017-09-20 16:29:02 +0000): > Hello > > RFC > > On some arches C function pointers are indirect and point to > a function descriptor, which contains the actual pointer to the code. > This mostly doesn't matter, except for cases when people want to print > out function pointers in symbolic format, because the usual '%pS/%ps' > does not work on those arches as expected. That's the reason why we > have '%pF/%pf', but since it's here because of a subtle ABI detail > specific to some arches (ppc64/ia64/parisc64) it's easy to misuse > '%pF/%pf' and '%pS/%ps' (see [1], for example). > > This patch set attempts to move ia64/ppc64/parisc64 C function > pointer ABI details out of printk() to arch code. Function dereference > code now checks if a pointer belongs to a .opd ELF section and dereferences > that pointer only if it does. The kernel and modules have their own .opd > sections that's why I use two different ARCH functions: for kernel and > for module pointer dereference. > > I planned to remove dereference_function_descriptor() entirely, > but then I discovered a bunch other uses cases (kgdbts, init/main.c, > extable, etc.), so I decided to keep dereference_function_descriptor() > around because the main point of this patch set is to deprecate %pF/%pf. > But at the same time, I think I can go further and handle both kernel > and module descriptor dereference in dereference_function_descriptor(). > We need a module pointer for module .opd check, so that will come at an > extra cost of module lookup (may be there will some other issues along > the way, haven't checked it). > > Right now we've got: > > - dereference_function_descriptor(addr) > a generic (old) function. it simply attempts to dereference > whatever pointer we give it. > > - dereference_kernel_function_descriptor(addr) > dereferences a kernel pointer if it's within the kernel's .opd > section. > > - dereference_module_function_descriptor(module, addr) > dereference a module pointer if it's within the module's .opd > section. > > > *** A BIG NOTE *** > I don't own ia64/ppc64/parisc64 hardware, so the patches are not > tested. Sorry about that! Tested patch series on ppc64 sucessfully. You may add tested by to the series. Tested-by: Santosh Sivaraj <santosh@xxxxxxxxxx> Thanks, Santosh > > Another note: > I need to check what is BPF symbol lookup and do we need to > do any dereference there. > > v2: > -- convert dereference_function_descriptor() to unsigned long > -- fix kernel descriptor range checks (Helge) > -- fix parisc module descriptor range check (Helge) > -- fix ppc64 module range check > -- add checkpatch patch > > > Sergey Senozhatsky (7): > switch dereference_function_descriptor() to `unsigned long' > sections: split dereference_function_descriptor() > ia64: Add .opd based function descriptor dereference > powerpc64: Add .opd based function descriptor dereference > parisc64: Add .opd based function descriptor dereference > symbol lookup: use new kernel and module dereference functions > checkpatch: add pF/pf deprecation warning > > Documentation/printk-formats.txt | 15 +++++---------- > arch/ia64/include/asm/sections.h | 16 ++++++++++++---- > arch/ia64/kernel/module.c | 13 +++++++++++++ > arch/ia64/kernel/vmlinux.lds.S | 2 ++ > arch/parisc/boot/compressed/vmlinux.lds.S | 2 ++ > arch/parisc/include/asm/sections.h | 4 +++- > arch/parisc/kernel/module.c | 17 +++++++++++++++++ > arch/parisc/kernel/process.c | 15 ++++++++++++--- > arch/parisc/kernel/vmlinux.lds.S | 2 ++ > arch/parisc/mm/init.c | 4 ++-- > arch/powerpc/include/asm/module.h | 3 +++ > arch/powerpc/include/asm/sections.h | 17 ++++++++++++++--- > arch/powerpc/kernel/module_64.c | 16 ++++++++++++++++ > arch/powerpc/kernel/vmlinux.lds.S | 2 ++ > drivers/misc/kgdbts.c | 2 +- > include/asm-generic/sections.h | 8 ++++++-- > include/linux/moduleloader.h | 4 ++++ > init/main.c | 2 +- > kernel/extable.c | 2 +- > kernel/kallsyms.c | 1 + > kernel/module.c | 9 ++++++++- > lib/vsprintf.c | 5 +---- > scripts/checkpatch.pl | 6 ++++-- > 23 files changed, 132 insertions(+), 35 deletions(-) --
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