6.1-stable review patch. If anyone has any objections, please let me know.
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From: John David Anglin dave.anglin@bell.net
commit cb22f247f371bd206a88cf0e0c05d80b8b62fb26 upstream.
The following testcase exposed a problem with our read access checks in get_user() and raw_copy_from_user():
#include <stdint.h> #include <stddef.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <errno.h> #include <sys/mman.h> #include <sys/types.h>
int main(int argc, char **argv) { unsigned long page_size = sysconf(_SC_PAGESIZE); char *p = malloc(3 * page_size); char *p_aligned;
/* initialize memory region. If not initialized, write syscall below will correctly return EFAULT. */ if (1) memset(p, 'X', 3 * page_size);
p_aligned = (char *) ((((uintptr_t) p) + (2*page_size - 1)) & ~(page_size - 1)); /* Drop PROT_READ protection. Kernel and userspace should fault when accessing that memory region */ mprotect(p_aligned, page_size, PROT_NONE);
/* the following write() should return EFAULT, since PROT_READ was dropped by previous mprotect() */ int ret = write(2, p_aligned, 1); if (!ret || errno != EFAULT) printf("\n FAILURE: write() did not returned expected EFAULT value\n");
return 0; }
Because of the way _PAGE_READ is handled, kernel code never generates a read access fault when it access a page as the kernel privilege level is always less than PL1 in the PTE.
This patch reworks the comments in the make_insert_tlb macro to try to make this clearer.
Signed-off-by: John David Anglin dave.anglin@bell.net Signed-off-by: Helge Deller deller@gmx.de Cc: stable@vger.kernel.org # v5.12+ Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/parisc/kernel/entry.S | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)
--- a/arch/parisc/kernel/entry.S +++ b/arch/parisc/kernel/entry.S @@ -486,6 +486,12 @@ * this happens is quite subtle, read below */ .macro make_insert_tlb spc,pte,prot,tmp space_to_prot \spc \prot /* create prot id from space */ + +#if _PAGE_SPECIAL_BIT == _PAGE_DMB_BIT + /* need to drop DMB bit, as it's used as SPECIAL flag */ + depi 0,_PAGE_SPECIAL_BIT,1,\pte +#endif + /* The following is the real subtlety. This is depositing * T <-> _PAGE_REFTRAP * D <-> _PAGE_DIRTY @@ -498,17 +504,18 @@ * Finally, _PAGE_READ goes in the top bit of PL1 (so we * trigger an access rights trap in user space if the user * tries to read an unreadable page */ -#if _PAGE_SPECIAL_BIT == _PAGE_DMB_BIT - /* need to drop DMB bit, as it's used as SPECIAL flag */ - depi 0,_PAGE_SPECIAL_BIT,1,\pte -#endif depd \pte,8,7,\prot
/* PAGE_USER indicates the page can be read with user privileges, * so deposit X1|11 to PL1|PL2 (remember the upper bit of PL1 - * contains _PAGE_READ) */ + * contains _PAGE_READ). While the kernel can't directly write + * user pages which have _PAGE_WRITE zero, it can read pages + * which have _PAGE_READ zero (PL <= PL1). Thus, the kernel + * exception fault handler doesn't trigger when reading pages + * that aren't user read accessible */ extrd,u,*= \pte,_PAGE_USER_BIT+32,1,%r0 depdi 7,11,3,\prot + /* If we're a gateway page, drop PL2 back to zero for promotion * to kernel privilege (so we can execute the page as kernel). * Any privilege promotion page always denys read and write */