Messages in this thread | | | Subject | Re: [PATCH v13 10/20] kernel, arm64: untag user pointers in prctl_set_mm* | From | Kevin Brodsky <> | Date | Thu, 21 Mar 2019 17:52:37 +0000 |
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On 20/03/2019 14:51, Andrey Konovalov wrote: > This patch is a part of a series that extends arm64 kernel ABI to allow to > pass tagged user pointers (with the top byte set to something else other > than 0x00) as syscall arguments. > > prctl_set_mm() and prctl_set_mm_map() use provided user pointers for vma > lookups and do some pointer comparisons to perform validation, which can > only by done with untagged pointers. > > Untag user pointers in these functions for vma lookup and validity checks. > > Signed-off-by: Andrey Konovalov <andreyknvl@google.com> > --- > kernel/sys.c | 44 ++++++++++++++++++++++++++++++-------------- > 1 file changed, 30 insertions(+), 14 deletions(-) > > diff --git a/kernel/sys.c b/kernel/sys.c > index 12df0e5434b8..fe26ccf3c9e6 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -1885,11 +1885,12 @@ static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd) > * WARNING: we don't require any capability here so be very careful > * in what is allowed for modification from userspace. > */ > -static int validate_prctl_map(struct prctl_mm_map *prctl_map) > +static int validate_prctl_map(struct prctl_mm_map *tagged_prctl_map) > { > unsigned long mmap_max_addr = TASK_SIZE; > struct mm_struct *mm = current->mm; > int error = -EINVAL, i; > + struct prctl_mm_map prctl_map; > > static const unsigned char offsets[] = { > offsetof(struct prctl_mm_map, start_code), > @@ -1905,12 +1906,25 @@ static int validate_prctl_map(struct prctl_mm_map *prctl_map) > offsetof(struct prctl_mm_map, env_end), > }; > > + memcpy(&prctl_map, tagged_prctl_map, sizeof(prctl_map)); > + prctl_map.start_code = untagged_addr(prctl_map.start_code); > + prctl_map.end_code = untagged_addr(prctl_map.end_code); > + prctl_map.start_data = untagged_addr(prctl_map.start_data); > + prctl_map.end_data = untagged_addr(prctl_map.end_data); > + prctl_map.start_brk = untagged_addr(prctl_map.start_brk); > + prctl_map.brk = untagged_addr(prctl_map.brk); > + prctl_map.start_stack = untagged_addr(prctl_map.start_stack); > + prctl_map.arg_start = untagged_addr(prctl_map.arg_start); > + prctl_map.arg_end = untagged_addr(prctl_map.arg_end); > + prctl_map.env_start = untagged_addr(prctl_map.env_start); > + prctl_map.env_end = untagged_addr(prctl_map.env_end); > + > /* > * Make sure the members are not somewhere outside > * of allowed address space. > */ > for (i = 0; i < ARRAY_SIZE(offsets); i++) { > - u64 val = *(u64 *)((char *)prctl_map + offsets[i]); > + u64 val = *(u64 *)((char *)&prctl_map + offsets[i]); > > if ((unsigned long)val >= mmap_max_addr || > (unsigned long)val < mmap_min_addr) > @@ -1921,8 +1935,8 @@ static int validate_prctl_map(struct prctl_mm_map *prctl_map) > * Make sure the pairs are ordered. > */ > #define __prctl_check_order(__m1, __op, __m2) \ > - ((unsigned long)prctl_map->__m1 __op \ > - (unsigned long)prctl_map->__m2) ? 0 : -EINVAL > + ((unsigned long)prctl_map.__m1 __op \ > + (unsigned long)prctl_map.__m2) ? 0 : -EINVAL > error = __prctl_check_order(start_code, <, end_code); > error |= __prctl_check_order(start_data, <, end_data); > error |= __prctl_check_order(start_brk, <=, brk); > @@ -1937,23 +1951,24 @@ static int validate_prctl_map(struct prctl_mm_map *prctl_map) > /* > * @brk should be after @end_data in traditional maps. > */ > - if (prctl_map->start_brk <= prctl_map->end_data || > - prctl_map->brk <= prctl_map->end_data) > + if (prctl_map.start_brk <= prctl_map.end_data || > + prctl_map.brk <= prctl_map.end_data) > goto out; > > /* > * Neither we should allow to override limits if they set. > */ > - if (check_data_rlimit(rlimit(RLIMIT_DATA), prctl_map->brk, > - prctl_map->start_brk, prctl_map->end_data, > - prctl_map->start_data)) > + if (check_data_rlimit(rlimit(RLIMIT_DATA), prctl_map.brk, > + prctl_map.start_brk, prctl_map.end_data, > + prctl_map.start_data)) > goto out; > > /* > * Someone is trying to cheat the auxv vector. > */ > - if (prctl_map->auxv_size) { > - if (!prctl_map->auxv || prctl_map->auxv_size > sizeof(mm->saved_auxv)) > + if (prctl_map.auxv_size) { > + if (!prctl_map.auxv || prctl_map.auxv_size > > + sizeof(mm->saved_auxv)) > goto out; > } > > @@ -1962,7 +1977,7 @@ static int validate_prctl_map(struct prctl_mm_map *prctl_map) > * change /proc/pid/exe link: only local sys admin should > * be allowed to. > */ > - if (prctl_map->exe_fd != (u32)-1) { > + if (prctl_map.exe_fd != (u32)-1) { > if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN)) > goto out; > } > @@ -2120,13 +2135,14 @@ static int prctl_set_mm(int opt, unsigned long addr, > if (opt == PR_SET_MM_AUXV) > return prctl_set_auxv(mm, addr, arg4); > > - if (addr >= TASK_SIZE || addr < mmap_min_addr) > + if (untagged_addr(addr) >= TASK_SIZE || > + untagged_addr(addr) < mmap_min_addr) > return -EINVAL; > > error = -EINVAL; > > down_write(&mm->mmap_sem); > - vma = find_vma(mm, addr); > + vma = find_vma(mm, untagged_addr(addr)); > > prctl_map.start_code = mm->start_code; > prctl_map.end_code = mm->end_code;
I think this new version is consistent w.r.t. tagged/untagged pointer usage. However, I also note that a significant change has been introduced: it is now possible to set MM fields to tagged addresses (tags are ignored by validate_prctl_map()). I am not opposed to this as such, but have you considered the implications? Does it make sense to have a tagged value for e.g. prctl_map.arg_start? Is the kernel able to handle tagged values in those fields? I have the feeling that it's safer to discard tags for now, and if necessary allow them to be preserved later on.
Kevin
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