On Tue, Oct 17, 2017 at 09:37:48AM +0200, Michal Hocko wrote: > On Mon 16-10-17 21:02:09, James Hogan wrote: > > On Mon, Oct 16, 2017 at 09:00:47PM +0200, Michal Hocko wrote: > > > [CCing metag people for the metag elf_map implementation specific. The thread > > > starts here http://lkml.kernel.org/r/20171016134446.19910-1-mhocko@xxxxxxxxxx] > > > > > > On Mon 16-10-17 09:39:14, Kees Cook wrote: > > > > On Mon, Oct 16, 2017 at 6:44 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > + return -EAGAIN; > > > > > + } > > > > > + > > > > > + return map_addr; > > > > > +} > > > > > + > > > > > static unsigned long elf_map(struct file *filep, unsigned long addr, > > > > > struct elf_phdr *eppnt, int prot, int type, > > > > > unsigned long total_size) > > > > > @@ -366,11 +389,11 @@ static unsigned long elf_map(struct file *filep, unsigned long addr, > > > > > > > > elf_map is redirected on metag -- it should probably have its vm_mmap > > > > calls adjust too. > > > > > > Thanks for spotting this. I am not really familiar with metag. It seems > > > to clear MAP_FIXED already > > > tcm_tag = tcm_lookup_tag(addr); > > > > > > if (tcm_tag != TCM_INVALID_TAG) > > > type &= ~MAP_FIXED; > > > > > > So if there is a tag the flag is cleared. I do not understand this code > > > (and git log doesn't help) but why is this MAP_FIXED code really needed? > > > > This function was added to the metag port in mid-2010 to support ELFs > > with tightly coupled memory (TCM) segments, for example metag "core" > > memories are at fixed virtual addresses and aren't MMU mappable (i.e. > > globally accessible), and are outside of the usual userland address > > range, but are as fast as cache. The commit message says this: > > > > > Override the definition of the elf_map() function to special case > > > sections that are loaded at the address of the internal memories. > > > If we have such a section, map it at a different address and copy > > > the contents of the section into the appropriate memory. > > > > So yeh, it looks like if the section is meant to use TCM based on the > > virtual address, it drops MAP_FIXED so that the vm_mmap can succeed > > (because its outside the normally valid range), and then copies it > > directly to the desired TCM so the program can use it. > > > > Hope that helps add some context to understand whats needed. > > Hmm, so IIUC then we need the same fix as > http://lkml.kernel.org/r/20171016134446.19910-2-mhocko@xxxxxxxxxx, > right? > > This would be something like. I wanted to share elf_vm_mmap but didn't > find a proper place to not cause include dependency hell so I balied out > to c&p. > --- > diff --git a/arch/metag/kernel/process.c b/arch/metag/kernel/process.c > index c4606ce743d2..b20596b4c4c2 100644 > --- a/arch/metag/kernel/process.c > +++ b/arch/metag/kernel/process.c > @@ -378,6 +378,29 @@ int dump_fpu(struct pt_regs *regs, elf_fpregset_t *fpu) > > #define BAD_ADDR(x) ((unsigned long)(x) >= TASK_SIZE) > > +static unsigned long elf_vm_mmap(struct file *filep, unsigned long addr, > + unsigned long size, int prot, int type, unsigned long off) > +{ > + unsigned long map_addr; > + > + /* > + * If caller requests the mapping at a specific place, make sure we fail > + * rather than potentially clobber an existing mapping which can have > + * security consequences (e.g. smash over the stack area). > + */ > + map_addr = vm_mmap(filep, addr, size, prot, type & ~MAP_FIXED, off); > + if (BAD_ADDR(map_addr)) > + return map_addr; > + > + if ((type & MAP_FIXED) && map_addr != addr) { > + pr_info("Uhuuh, elf segement at %p requested but the memory is mapped already\n", > + (void*)addr); > + return -EAGAIN; > + } > + > + return map_addr; > +} > + > unsigned long __metag_elf_map(struct file *filep, unsigned long addr, > struct elf_phdr *eppnt, int prot, int type, > unsigned long total_size) > @@ -410,11 +433,11 @@ unsigned long __metag_elf_map(struct file *filep, unsigned long addr, > */ > if (total_size) { > total_size = ELF_PAGEALIGN(total_size); > - map_addr = vm_mmap(filep, addr, total_size, prot, type, off); > + map_addr = elf_vm_mmap(filep, addr, total_size, prot, type, off); > if (!BAD_ADDR(map_addr)) > vm_munmap(map_addr+size, total_size-size); > } else > - map_addr = vm_mmap(filep, addr, size, prot, type, off); > + map_addr = elf_vm_mmap(filep, addr, size, prot, type, off); > > if (!BAD_ADDR(map_addr) && tcm_tag != TCM_INVALID_TAG) { > struct tcm_allocation *tcm; Yeh that looks reasonable to me. Cheers James
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