| Message ID | 1509465082-30427-4-git-send-email-Dave.Martin@arm.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v5,01/30] regset: Add support for dynamically sized regsets | expand |
On Tue, Oct 31, 2017 at 03:50:55PM +0000, Dave P Martin wrote: > Currently sys_rt_sigreturn() verifies that the base sigframe is > readable, but no similar check is performed on the extra data to > which an extra_context record points. > > This matters because the extra data will be read with the > unprotected user accessors. However, this is not a problem at > present because the extra data base address is required to be > exactly at the end of the base sigframe. So, there would need to > be a non-user-readable kernel address within about 59K > (SIGFRAME_MAXSZ - sizeof(struct rt_sigframe)) of some address for > which access_ok(VERIFY_READ) returns true, in order for sigreturn > to be able to read kernel memory that should be inaccessible to the > user task. This is currently impossible due to the untranslatable > address hole between the TTBR0 and TTBR1 address ranges. > > Disappearance of the hole between the TTBR0 and TTBR1 mapping > ranges would require the VA size for TTBR0 and TTBR1 to grow to at > least 55 bits, and either the disabling of tagged pointers for > userspace or enabling of tagged pointers for kernel space; none of > which is currently envisaged. > > Even so, it is wrong to use the unprotected user accessors without > an accompanying access_ok() check. > > To avoid the potential for future surprises, this patch does an > explicit access_ok() check on the extra data space when parsing an > extra_context record. > > Fixes: 33f082614c34 ("arm64: signal: Allow expansion of the signal frame") > Signed-off-by: Dave Martin <Dave.Martin@arm.com> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 0bdc96c..4716729 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -343,6 +343,10 @@ static int parse_user_sigframe(struct user_ctxs *user, */ offset = 0; limit = extra_size; + + if (!access_ok(VERIFY_READ, base, limit)) + goto invalid; + continue; default:
Currently sys_rt_sigreturn() verifies that the base sigframe is readable, but no similar check is performed on the extra data to which an extra_context record points. This matters because the extra data will be read with the unprotected user accessors. However, this is not a problem at present because the extra data base address is required to be exactly at the end of the base sigframe. So, there would need to be a non-user-readable kernel address within about 59K (SIGFRAME_MAXSZ - sizeof(struct rt_sigframe)) of some address for which access_ok(VERIFY_READ) returns true, in order for sigreturn to be able to read kernel memory that should be inaccessible to the user task. This is currently impossible due to the untranslatable address hole between the TTBR0 and TTBR1 address ranges. Disappearance of the hole between the TTBR0 and TTBR1 mapping ranges would require the VA size for TTBR0 and TTBR1 to grow to at least 55 bits, and either the disabling of tagged pointers for userspace or enabling of tagged pointers for kernel space; none of which is currently envisaged. Even so, it is wrong to use the unprotected user accessors without an accompanying access_ok() check. To avoid the potential for future surprises, this patch does an explicit access_ok() check on the extra data space when parsing an extra_context record. Fixes: 33f082614c34 ("arm64: signal: Allow expansion of the signal frame") Signed-off-by: Dave Martin <Dave.Martin@arm.com> --- arch/arm64/kernel/signal.c | 4 ++++ 1 file changed, 4 insertions(+)