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target/arm: Implement secure function return

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Secure function return happens when a non-secure function has been
called using BLXNS and so has a particular magic LR value (either
0xfefffffe or 0xfeffffff). The function return via BX behaves
specially when the new PC value is this magic value, in the same
way that exception returns are handled.

Adjust our BX excret guards so that they recognize the function
return magic number as well, and perform the function-return
unstacking in do_v7m_exception_exit().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 1507556919-24992-5-git-send-email-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2017-10-09 14:48:34 +01:00
parent 3e3fa230e3
commit d02a8698d7
3 changed files with 126 additions and 10 deletions
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7
target/arm/internals.h
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@ -72,6 +72,13 @@ FIELD(V7M_EXCRET, DCRS, 5, 1)
FIELD(V7M_EXCRET, S, 6, 1)
FIELD(V7M_EXCRET, RES1, 7, 25) /* including the must-be-1 prefix */
/* Minimum value which is a magic number for exception return */
#define EXC_RETURN_MIN_MAGIC 0xff000000
/* Minimum number which is a magic number for function or exception return
* when using v8M security extension
*/
#define FNC_RETURN_MIN_MAGIC 0xfefffffe
/* We use a few fake FSR values for internal purposes in M profile.
* M profile cores don't have A/R format FSRs, but currently our
* get_phys_addr() code assumes A/R profile and reports failures via