Arch arm userspace syscalls stack fix #17146
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ioannisg
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andrewboie,
andyross,
galak and
MaureenHelm
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I think this one should be back-ported to the LTS |
andrewboie
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Jun 28, 2019
26 tasks
System call arguments are indexed from 1 to 6, so arg0 is corrected to arg1 in two occasions. In addition, the ARM function for system calls is now called z_arm_do_syscall, so we update the inline comment in __svc handler. Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
We need to correct the inline comment in swap_helper.S, which is suggesting that system call attempts with invalid syscall IDs (i.e. above the limit) do not force the CPU to elevate privileges. This is in fact not true, since the execution flow moves into valid syscall ID handling. In other words, all we do for system calls with invalid ID numbers is to treat them as valid syscalls with the K_SYSCALL_BAD ID value. We fix the inline documentation to reflect the actual execution flow. Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
z_arm_do_syscall is executing in privileged mode. This implies that we shall not be allowed to use the thread's default unprivileged stack, (i.e push to or pop from it), to avoid any possible stack corruptions. Note that since we execute in PRIV mode and no MPU guard or PSPLIM register is guarding the end of the default stack, we won't be able to detect any stack overflows. This commit implement the above change, by forcing z_arm_do_syscall() to FIRST switch to privileged stack and then do all the preparations to execute the system call. Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
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In addition to some minor typo fixes, this patch forces z_arm_do_syscall to only use the privilege stack for system calls.
Fixes #17177