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([71.212.149.95]) by smtp.gmail.com with ESMTPSA id g9-20020aa796a9000000b006be5af77f06sm3881690pfk.2.2023.10.18.16.31.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Oct 2023 16:31:37 -0700 (PDT) From: Richard Henderson To: qemu-devel@nongnu.org Cc: Mikulas Patocka , qemu-stable@nongnu.org, Yoshinori Sato Subject: [PULL 03/14] linux-user/sh4: Fix crashes on signal delivery Date: Wed, 18 Oct 2023 16:31:23 -0700 Message-Id: <20231018233134.1594292-4-richard.henderson@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231018233134.1594292-1-richard.henderson@linaro.org> References: <20231018233134.1594292-1-richard.henderson@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2607:f8b0:4864:20::c2b; envelope-from=richard.henderson@linaro.org; helo=mail-oo1-xc2b.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patch=linaro.org@nongnu.org Sender: qemu-devel-bounces+patch=linaro.org@nongnu.org From: Mikulas Patocka sh4 uses gUSA (general UserSpace Atomicity) to provide atomicity on CPUs that don't have atomic instructions. A gUSA region that adds 1 to an atomic variable stored in @R2 looks like this: 4004b6: 03 c7 mova 4004c4 ,r0 4004b8: f3 61 mov r15,r1 4004ba: 09 00 nop 4004bc: fa ef mov #-6,r15 4004be: 22 63 mov.l @r2,r3 4004c0: 01 73 add #1,r3 4004c2: 32 22 mov.l r3,@r2 4004c4: 13 6f mov r1,r15 R0 contains a pointer to the end of the gUSA region R1 contains the saved stack pointer R15 contains negative length of the gUSA region When this region is interrupted by a signal, the kernel detects if R15 >= -128U. If yes, the kernel rolls back PC to the beginning of the region and restores SP by copying R1 to R15. The problem happens if we are interrupted by a signal at address 4004c4. R15 still holds the value -6, but the atomic value was already written by an instruction at address 4004c2. In this situation we can't undo the gUSA. The function unwind_gusa does nothing, the signal handler attempts to push a signal frame to the address -6 and crashes. This patch fixes it, so that if we are interrupted at the last instruction in a gUSA region, we copy R1 to R15 to restore the correct stack pointer and avoid crashing. There's another bug: if we are interrupted in a delay slot, we save the address of the instruction in the delay slot. We must save the address of the previous instruction. Cc: qemu-stable@nongnu.org Signed-off-by: Mikulas Patocka Reviewed-by: Yoshinori Sato Message-Id: Reviewed-by: Richard Henderson Signed-off-by: Richard Henderson --- linux-user/sh4/signal.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/linux-user/sh4/signal.c b/linux-user/sh4/signal.c index c4ba962708..c16c2c2d57 100644 --- a/linux-user/sh4/signal.c +++ b/linux-user/sh4/signal.c @@ -104,6 +104,14 @@ static void unwind_gusa(CPUSH4State *regs) /* Reset the SP to the saved version in R1. */ regs->gregs[15] = regs->gregs[1]; + } else if (regs->gregs[15] >= -128u && regs->pc == regs->gregs[0]) { + /* If we are on the last instruction of a gUSA region, we must reset + the SP, otherwise we would be pushing the signal context to + invalid memory. */ + regs->gregs[15] = regs->gregs[1]; + } else if (regs->flags & TB_FLAG_DELAY_SLOT) { + /* If we are in a delay slot, push the previous instruction. */ + regs->pc -= 2; } }