Re: [PATCH] fs/binfmt_elf_fdpic.c: fix brk area overlap with stack on NOMMU
Hi Rich, On 15/09/15 01:17, Rich Felker wrote: > On Mon, Sep 14, 2015 at 10:13:03PM +1000, Greg Ungerer wrote: >> On 26/08/15 11:26, Greg Ungerer wrote: >>> On 21/08/15 05:11, Rich Felker wrote: From: Rich Felker On NOMMU archs, the FDPIC ELF loader sets up the usable brk range to overlap with all but the last PAGE_SIZE bytes of the stack. This leads to catastrophic memory reuse/corruption if brk is used. Fix by setting the brk area to zero size to disable its use. Signed-off-by: Rich Felker >>> >>> It would make sense to run this by David Howells , >>> I think he wrote this code (added to CC list). >>> >>> I have no problem with it, so: >>> >>> Acked-by: Greg Ungerer >> >> Has anybody picked this up to push to Linus? >> If not I can take it via the m68knommu tree. > > As far as I know, no. If you can do it that would be great. Patch applied to m68knommu git tree (for-next branch). (https://git.kernel.org/cgit/linux/kernel/git/gerg/m68knommu.git/) Regards Greg --- There is no reason for the kernel to be providing a brk area at all on NOMMU; the bFLT loader does not provide one, uClibc never uses brk on NOMMU targets, and musl libc goes out of its way to avoid using brk that might run into the stack. >>> >>> I recall a long time back someone was playing with the idea of setting >>> the brk to the unused parts of the last data area page. (Somewhat like >>> this code seems to be trying). That scheme still allocated the full >>> requested stack size (IIRC) though. And that would have been on bFLT >>> executables. Anyway, just some historical reference, not really >>> relevant now. >>> >>> Regards >>> Greg >>> >>> >>> --- fs/binfmt_elf_fdpic.c.orig 2015-08-20 18:05:19.089888654 + +++ fs/binfmt_elf_fdpic.c 2015-08-20 18:10:01.519871432 + @@ -374,10 +388,7 @@ static int load_elf_fdpic_binary(struct PAGE_ALIGN(current->mm->start_brk); #else - /* create a stack and brk area big enough for everyone - * - the brk heap starts at the bottom and works up - * - the stack starts at the top and works down - */ + /* create a stack area and zero-size brk area */ stack_size = (stack_size + PAGE_SIZE - 1) & PAGE_MASK; if (stack_size < PAGE_SIZE * 2) stack_size = PAGE_SIZE * 2; @@ -400,8 +411,6 @@ static int load_elf_fdpic_binary(struct current->mm->brk = current->mm->start_brk; current->mm->context.end_brk = current->mm->start_brk; - current->mm->context.end_brk += - (stack_size > PAGE_SIZE) ? (stack_size - PAGE_SIZE) : 0; current->mm->start_stack = current->mm->start_brk + stack_size; #endif >>> > -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] fs/binfmt_elf_fdpic.c: fix brk area overlap with stack on NOMMU
On Mon, Sep 14, 2015 at 10:13:03PM +1000, Greg Ungerer wrote: > Hi Rich, > > > On 26/08/15 11:26, Greg Ungerer wrote: > >On 21/08/15 05:11, Rich Felker wrote: > >>From: Rich Felker > >> > >>On NOMMU archs, the FDPIC ELF loader sets up the usable brk range to > >>overlap with all but the last PAGE_SIZE bytes of the stack. This leads > >>to catastrophic memory reuse/corruption if brk is used. Fix by setting > >>the brk area to zero size to disable its use. > >> > >>Signed-off-by: Rich Felker > > > >It would make sense to run this by David Howells , > >I think he wrote this code (added to CC list). > > > >I have no problem with it, so: > > > >Acked-by: Greg Ungerer > > Has anybody picked this up to push to Linus? > If not I can take it via the m68knommu tree. As far as I know, no. If you can do it that would be great. Rich > >>--- > >> > >>There is no reason for the kernel to be providing a brk area at all on > >>NOMMU; the bFLT loader does not provide one, uClibc never uses brk on > >>NOMMU targets, and musl libc goes out of its way to avoid using brk > >>that might run into the stack. > > > >I recall a long time back someone was playing with the idea of setting > >the brk to the unused parts of the last data area page. (Somewhat like > >this code seems to be trying). That scheme still allocated the full > >requested stack size (IIRC) though. And that would have been on bFLT > >executables. Anyway, just some historical reference, not really > >relevant now. > > > >Regards > >Greg > > > > > > > >>--- fs/binfmt_elf_fdpic.c.orig 2015-08-20 18:05:19.089888654 + > >>+++ fs/binfmt_elf_fdpic.c 2015-08-20 18:10:01.519871432 + > >>@@ -374,10 +388,7 @@ static int load_elf_fdpic_binary(struct > >>PAGE_ALIGN(current->mm->start_brk); > >> > >> #else > >>- /* create a stack and brk area big enough for everyone > >>-* - the brk heap starts at the bottom and works up > >>-* - the stack starts at the top and works down > >>-*/ > >>+ /* create a stack area and zero-size brk area */ > >>stack_size = (stack_size + PAGE_SIZE - 1) & PAGE_MASK; > >>if (stack_size < PAGE_SIZE * 2) > >>stack_size = PAGE_SIZE * 2; > >>@@ -400,8 +411,6 @@ static int load_elf_fdpic_binary(struct > >> > >>current->mm->brk = current->mm->start_brk; > >>current->mm->context.end_brk = current->mm->start_brk; > >>- current->mm->context.end_brk += > >>- (stack_size > PAGE_SIZE) ? (stack_size - PAGE_SIZE) : 0; > >>current->mm->start_stack = current->mm->start_brk + stack_size; > >> #endif > >> > >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] fs/binfmt_elf_fdpic.c: fix brk area overlap with stack on NOMMU
Hi Rich, On 26/08/15 11:26, Greg Ungerer wrote: On 21/08/15 05:11, Rich Felker wrote: From: Rich Felker On NOMMU archs, the FDPIC ELF loader sets up the usable brk range to overlap with all but the last PAGE_SIZE bytes of the stack. This leads to catastrophic memory reuse/corruption if brk is used. Fix by setting the brk area to zero size to disable its use. Signed-off-by: Rich Felker It would make sense to run this by David Howells , I think he wrote this code (added to CC list). I have no problem with it, so: Acked-by: Greg Ungerer Has anybody picked this up to push to Linus? If not I can take it via the m68knommu tree. Regards Greg --- There is no reason for the kernel to be providing a brk area at all on NOMMU; the bFLT loader does not provide one, uClibc never uses brk on NOMMU targets, and musl libc goes out of its way to avoid using brk that might run into the stack. I recall a long time back someone was playing with the idea of setting the brk to the unused parts of the last data area page. (Somewhat like this code seems to be trying). That scheme still allocated the full requested stack size (IIRC) though. And that would have been on bFLT executables. Anyway, just some historical reference, not really relevant now. Regards Greg --- fs/binfmt_elf_fdpic.c.orig 2015-08-20 18:05:19.089888654 + +++ fs/binfmt_elf_fdpic.c 2015-08-20 18:10:01.519871432 + @@ -374,10 +388,7 @@ static int load_elf_fdpic_binary(struct PAGE_ALIGN(current->mm->start_brk); #else - /* create a stack and brk area big enough for everyone -* - the brk heap starts at the bottom and works up -* - the stack starts at the top and works down -*/ + /* create a stack area and zero-size brk area */ stack_size = (stack_size + PAGE_SIZE - 1) & PAGE_MASK; if (stack_size < PAGE_SIZE * 2) stack_size = PAGE_SIZE * 2; @@ -400,8 +411,6 @@ static int load_elf_fdpic_binary(struct current->mm->brk = current->mm->start_brk; current->mm->context.end_brk = current->mm->start_brk; - current->mm->context.end_brk += - (stack_size > PAGE_SIZE) ? (stack_size - PAGE_SIZE) : 0; current->mm->start_stack = current->mm->start_brk + stack_size; #endif -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] fs/binfmt_elf_fdpic.c: fix brk area overlap with stack on NOMMU
Greg Ungerer wrote: > It would make sense to run this by David Howells , > I think he wrote this code (added to CC list). > > I have no problem with it, so: Fine by me too. Acked-by: David Howells -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] fs/binfmt_elf_fdpic.c: fix brk area overlap with stack on NOMMU
On Wed, Aug 26, 2015 at 11:26:02AM +1000, Greg Ungerer wrote: > Hi Rich, > > On 21/08/15 05:11, Rich Felker wrote: > > From: Rich Felker > > > > On NOMMU archs, the FDPIC ELF loader sets up the usable brk range to > > overlap with all but the last PAGE_SIZE bytes of the stack. This leads > > to catastrophic memory reuse/corruption if brk is used. Fix by setting > > the brk area to zero size to disable its use. > > > > Signed-off-by: Rich Felker > > It would make sense to run this by David Howells , > I think he wrote this code (added to CC list). Thanks. I have another follow-up patch to submit soon that uses the existing ELF_FDPIC_FLAG_CONSTDISP code in binfmt_elf_fdpic.c to load normal, non-FDPIC ELF files on NOMMU, so I'll make sure to CC him on that too. > I have no problem with it, so: > > Acked-by: Greg Ungerer > > > --- > > > > There is no reason for the kernel to be providing a brk area at all on > > NOMMU; the bFLT loader does not provide one, uClibc never uses brk on > > NOMMU targets, and musl libc goes out of its way to avoid using brk > > that might run into the stack. > > I recall a long time back someone was playing with the idea of setting > the brk to the unused parts of the last data area page. (Somewhat like > this code seems to be trying). That scheme still allocated the full > requested stack size (IIRC) though. And that would have been on bFLT > executables. Anyway, just some historical reference, not really > relevant now. For what it's worth, musl's malloc rounds the initial brk up to a page boundary, but the dynamic linker recovers any partial page at the end of the data segment and donates it to malloc without brk's help. So even though brk will fail and malloc will fall back to mmap, this otherwise-wasted space does get recovered and used. Rich -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] fs/binfmt_elf_fdpic.c: fix brk area overlap with stack on NOMMU
Hi Rich, On 21/08/15 05:11, Rich Felker wrote: > From: Rich Felker > > On NOMMU archs, the FDPIC ELF loader sets up the usable brk range to > overlap with all but the last PAGE_SIZE bytes of the stack. This leads > to catastrophic memory reuse/corruption if brk is used. Fix by setting > the brk area to zero size to disable its use. > > Signed-off-by: Rich Felker It would make sense to run this by David Howells , I think he wrote this code (added to CC list). I have no problem with it, so: Acked-by: Greg Ungerer > --- > > There is no reason for the kernel to be providing a brk area at all on > NOMMU; the bFLT loader does not provide one, uClibc never uses brk on > NOMMU targets, and musl libc goes out of its way to avoid using brk > that might run into the stack. I recall a long time back someone was playing with the idea of setting the brk to the unused parts of the last data area page. (Somewhat like this code seems to be trying). That scheme still allocated the full requested stack size (IIRC) though. And that would have been on bFLT executables. Anyway, just some historical reference, not really relevant now. Regards Greg > --- fs/binfmt_elf_fdpic.c.orig2015-08-20 18:05:19.089888654 + > +++ fs/binfmt_elf_fdpic.c 2015-08-20 18:10:01.519871432 + > @@ -374,10 +388,7 @@ static int load_elf_fdpic_binary(struct > PAGE_ALIGN(current->mm->start_brk); > > #else > - /* create a stack and brk area big enough for everyone > - * - the brk heap starts at the bottom and works up > - * - the stack starts at the top and works down > - */ > + /* create a stack area and zero-size brk area */ > stack_size = (stack_size + PAGE_SIZE - 1) & PAGE_MASK; > if (stack_size < PAGE_SIZE * 2) > stack_size = PAGE_SIZE * 2; > @@ -400,8 +411,6 @@ static int load_elf_fdpic_binary(struct > > current->mm->brk = current->mm->start_brk; > current->mm->context.end_brk = current->mm->start_brk; > - current->mm->context.end_brk += > - (stack_size > PAGE_SIZE) ? (stack_size - PAGE_SIZE) : 0; > current->mm->start_stack = current->mm->start_brk + stack_size; > #endif > > -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
