4.18-stable review patch. If anyone has any objections, please let me know.
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From: Ram Pai linuxram@us.ibm.com
commit a57a04c76e06822e4377831611364c846b7202ca upstream.
Currently in a multithreaded application, a key allocated by one thread is not usable by other threads. By "not usable" we mean that other threads are unable to change the access permissions for that key for themselves.
When a new key is allocated in one thread, the corresponding UAMOR bits for that thread get enabled, however the UAMOR bits for that key for all other threads remain disabled.
Other threads have no way to set permissions on the key, and the current default permissions are that read/write is enabled for all keys, which means the key has no effect for other threads. Although that may be the desired behaviour in some circumstances, having all threads able to control their permissions for the key is more flexible.
The current behaviour also differs from the x86 behaviour, which is problematic for users.
To fix this, enable the UAMOR bits for all keys, at process creation (in start_thread(), ie exec time). Since the contents of UAMOR are inherited at fork, all threads are capable of modifying the permissions on any key.
This is technically an ABI break on powerpc, but pkey support is fairly new on powerpc and not widely used, and this brings us into line with x86.
Fixes: cf43d3b26452 ("powerpc: Enable pkey subsystem") Cc: stable@vger.kernel.org # v4.16+ Tested-by: Florian Weimer fweimer@redhat.com Signed-off-by: Ram Pai linuxram@us.ibm.com [mpe: Reword some of the changelog] Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/mm/pkeys.c | 44 ++++++++++++++++++++++++++------------------ 1 file changed, 26 insertions(+), 18 deletions(-)
--- a/arch/powerpc/mm/pkeys.c +++ b/arch/powerpc/mm/pkeys.c @@ -15,8 +15,9 @@ bool pkey_execute_disable_supported; int pkeys_total; /* Total pkeys as per device tree */ bool pkeys_devtree_defined; /* pkey property exported by device tree */ u32 initial_allocation_mask; /* Bits set for reserved keys */ -u64 pkey_amr_uamor_mask; /* Bits in AMR/UMOR not to be touched */ +u64 pkey_amr_mask; /* Bits in AMR not to be touched */ u64 pkey_iamr_mask; /* Bits in AMR not to be touched */ +u64 pkey_uamor_mask; /* Bits in UMOR not to be touched */
#define AMR_BITS_PER_PKEY 2 #define AMR_RD_BIT 0x1UL @@ -119,20 +120,26 @@ int pkey_initialize(void) #else os_reserved = 0; #endif - initial_allocation_mask = ~0x0; - pkey_amr_uamor_mask = ~0x0ul; + initial_allocation_mask = (0x1 << 0) | (0x1 << 1); + + /* register mask is in BE format */ + pkey_amr_mask = ~0x0ul; pkey_iamr_mask = ~0x0ul; - /* - * key 0, 1 are reserved. - * key 0 is the default key, which allows read/write/execute. - * key 1 is recommended not to be used. PowerISA(3.0) page 1015, - * programming note. - */ - for (i = 2; i < (pkeys_total - os_reserved); i++) { - initial_allocation_mask &= ~(0x1 << i); - pkey_amr_uamor_mask &= ~(0x3ul << pkeyshift(i)); + + for (i = 0; i < (pkeys_total - os_reserved); i++) { + pkey_amr_mask &= ~(0x3ul << pkeyshift(i)); pkey_iamr_mask &= ~(0x1ul << pkeyshift(i)); } + + pkey_uamor_mask = ~0x0ul; + pkey_uamor_mask &= ~(0x3ul << pkeyshift(0)); + + /* mark the rest of the keys as reserved and hence unavailable */ + for (i = (pkeys_total - os_reserved); i < pkeys_total; i++) { + initial_allocation_mask |= (0x1 << i); + pkey_uamor_mask &= ~(0x3ul << pkeyshift(i)); + } + return 0; }
@@ -289,9 +296,6 @@ void thread_pkey_regs_restore(struct thr if (static_branch_likely(&pkey_disabled)) return;
- /* - * TODO: Just set UAMOR to zero if @new_thread hasn't used any keys yet. - */ if (old_thread->amr != new_thread->amr) write_amr(new_thread->amr); if (old_thread->iamr != new_thread->iamr) @@ -305,9 +309,13 @@ void thread_pkey_regs_init(struct thread if (static_branch_likely(&pkey_disabled)) return;
- thread->amr = read_amr() & pkey_amr_uamor_mask; - thread->iamr = read_iamr() & pkey_iamr_mask; - thread->uamor = read_uamor() & pkey_amr_uamor_mask; + thread->amr = pkey_amr_mask; + thread->iamr = pkey_iamr_mask; + thread->uamor = pkey_uamor_mask; + + write_uamor(pkey_uamor_mask); + write_amr(pkey_amr_mask); + write_iamr(pkey_iamr_mask); }
static inline bool pkey_allows_readwrite(int pkey)