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riscv: prevent stack corruption by reserving task_pt_regs(p) early
Early function calls, such as setup_vm(), relocate_enable_mmu(), soc_early_init() etc, are free to operate on stack. However, PT_SIZE_ON_STACK bytes at the head of the kernel stack are purposedly reserved for the placement of per-task register context pointed by task_pt_regs(p). Those functions may corrupt task_pt_regs if we overlap the $sp with it. In fact, we had accidentally corrupted sstatus.VS in some tests, treating the kernel to save V context before V was actually allocated, resulting in a kernel panic. Thus, we should skip PT_SIZE_ON_STACK for $sp before making C function calls from the top-level assembly. Co-developed-by: ShihPo Hung <shihpo.hung@sifive.com> Signed-off-by: ShihPo Hung <shihpo.hung@sifive.com> Co-developed-by: Vincent Chen <vincent.chen@sifive.com> Signed-off-by: Vincent Chen <vincent.chen@sifive.com> Signed-off-by: Greentime Hu <greentime.hu@sifive.com> Signed-off-by: Andy Chiu <andy.chiu@sifive.com> Reviewed-by: Conor Dooley <conor.dooley@microchip.com> Reviewed-by: Heiko Stuebner <heiko.stuebner@vrull.eu> Tested-by: Heiko Stuebner <heiko.stuebner@vrull.eu> Link: https://lore.kernel.org/r/20230605110724.21391-18-andy.chiu@sifive.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
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@ -301,6 +301,7 @@ clear_bss_done:
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la tp, init_task
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la sp, init_thread_union + THREAD_SIZE
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XIP_FIXUP_OFFSET sp
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addi sp, sp, -PT_SIZE_ON_STACK
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#ifdef CONFIG_BUILTIN_DTB
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la a0, __dtb_start
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XIP_FIXUP_OFFSET a0
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@ -318,6 +319,7 @@ clear_bss_done:
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/* Restore C environment */
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la tp, init_task
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la sp, init_thread_union + THREAD_SIZE
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addi sp, sp, -PT_SIZE_ON_STACK
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#ifdef CONFIG_KASAN
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call kasan_early_init
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