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arm64: entry: avoid writing lr explicitly for constructing return paths
Using an explicit adr instruction to set the link register to point at ret_fast_syscall/ret_to_user can defeat branch and return stack predictors. Instead, use the standard calling instructions (bl, blr) and have an unconditional branch as the following instruction. Signed-off-by: Will Deacon <will.deacon@arm.com>
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@ -455,8 +455,8 @@ el0_da:
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bic x0, x26, #(0xff << 56)
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mov x1, x25
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mov x2, sp
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adr lr, ret_to_user
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b do_mem_abort
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bl do_mem_abort
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b ret_to_user
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el0_ia:
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/*
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* Instruction abort handling
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@ -468,8 +468,8 @@ el0_ia:
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mov x0, x26
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orr x1, x25, #1 << 24 // use reserved ISS bit for instruction aborts
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mov x2, sp
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adr lr, ret_to_user
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b do_mem_abort
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bl do_mem_abort
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b ret_to_user
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el0_fpsimd_acc:
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/*
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* Floating Point or Advanced SIMD access
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@ -478,8 +478,8 @@ el0_fpsimd_acc:
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ct_user_exit
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mov x0, x25
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mov x1, sp
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adr lr, ret_to_user
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b do_fpsimd_acc
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bl do_fpsimd_acc
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b ret_to_user
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el0_fpsimd_exc:
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/*
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* Floating Point or Advanced SIMD exception
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@ -488,8 +488,8 @@ el0_fpsimd_exc:
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ct_user_exit
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mov x0, x25
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mov x1, sp
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adr lr, ret_to_user
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b do_fpsimd_exc
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bl do_fpsimd_exc
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b ret_to_user
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el0_sp_pc:
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/*
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* Stack or PC alignment exception handling
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@ -500,8 +500,8 @@ el0_sp_pc:
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mov x0, x26
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mov x1, x25
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mov x2, sp
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adr lr, ret_to_user
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b do_sp_pc_abort
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bl do_sp_pc_abort
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b ret_to_user
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el0_undef:
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/*
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* Undefined instruction
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@ -510,8 +510,8 @@ el0_undef:
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enable_dbg_and_irq
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ct_user_exit
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mov x0, sp
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adr lr, ret_to_user
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b do_undefinstr
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bl do_undefinstr
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b ret_to_user
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el0_dbg:
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/*
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* Debug exception handling
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@ -530,8 +530,8 @@ el0_inv:
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mov x0, sp
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mov x1, #BAD_SYNC
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mrs x2, esr_el1
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adr lr, ret_to_user
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b bad_mode
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bl bad_mode
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b ret_to_user
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ENDPROC(el0_sync)
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.align 6
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@ -653,14 +653,15 @@ el0_svc_naked: // compat entry point
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ldr x16, [tsk, #TI_FLAGS] // check for syscall hooks
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tst x16, #_TIF_SYSCALL_WORK
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b.ne __sys_trace
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adr lr, ret_fast_syscall // return address
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cmp scno, sc_nr // check upper syscall limit
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b.hs ni_sys
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ldr x16, [stbl, scno, lsl #3] // address in the syscall table
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br x16 // call sys_* routine
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blr x16 // call sys_* routine
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b ret_fast_syscall
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ni_sys:
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mov x0, sp
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b do_ni_syscall
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bl do_ni_syscall
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b ret_fast_syscall
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ENDPROC(el0_svc)
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/*
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@ -670,17 +671,16 @@ ENDPROC(el0_svc)
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__sys_trace:
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mov x0, sp
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bl syscall_trace_enter
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adr lr, __sys_trace_return // return address
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uxtw scno, w0 // syscall number (possibly new)
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mov x1, sp // pointer to regs
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cmp scno, sc_nr // check upper syscall limit
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b.hs ni_sys
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b.hs __ni_sys_trace
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ldp x0, x1, [sp] // restore the syscall args
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ldp x2, x3, [sp, #S_X2]
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ldp x4, x5, [sp, #S_X4]
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ldp x6, x7, [sp, #S_X6]
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ldr x16, [stbl, scno, lsl #3] // address in the syscall table
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br x16 // call sys_* routine
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blr x16 // call sys_* routine
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__sys_trace_return:
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str x0, [sp] // save returned x0
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@ -688,6 +688,11 @@ __sys_trace_return:
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bl syscall_trace_exit
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b ret_to_user
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__ni_sys_trace:
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mov x0, sp
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bl do_ni_syscall
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b __sys_trace_return
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/*
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* Special system call wrappers.
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*/
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